Summary: Envelope glycoprotein GP120

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Wikipedia: Envelope glycoprotein GP120
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Envelope glycoprotein GP120

Identifiers

Symbol

GP120

Available protein structures:
Pfam	structures
PDB	RCSB PDB; PDBe
PDBsum	structure summary

Envelope glycoprotein GP120 (or gp120) is a glycoprotein exposed on the surface of the HIV envelope. The 120 in its name comes from its molecular weight of 120 kilodaltons. gp120 is essential for virus entry into cells as it plays a vital role in seeking out specific cell surface receptors for entry.

The crystal structure of gp120 complexed to D1D2 CD4 and a neutralizing antibody Fab was solved by Peter Kwong in 1998. It is organized with an outer domain, an inner domain with respect to its termini and a bridging sheet. The gp120 gene, env, is around 1.5 kb long and codes for around 500 amino acids.^[1] Three gp120s, bound as heterodimers to a transmembrane glycoprotein, gp41, are thought to combine in a trimer to form the envelope spike,^[2] which is involved in virus-cell attachment.

The Human Immunodeficiency Virus (HIV) can mutate frequently to stay ahead of the immune system. There is however a highly conserved region in the virus genome near its receptor binding site. The glycoprotein gp120 is anchored to the viral membrane, or envelope, via non-covalent bonds with the transmembrane glycoprotein, gp41. It is involved in entry into cells by binding to CD4 receptors, particularly helper T-cells. Binding to CD4 is mainly electrostatic although there are van der Waals interactions and hydrogen bonds.

[edit] Variability

Since gp120 plays a vital role in the ability of HIV-1 to enter CD4⁺ cells, its evolution is of particular interest. Many neutralizing antibodies bind to sites located in variable regions of gp120, so mutations in these regions will be selected for strongly.^[3] The diversity of env has been shown to increase by 1-2% per year in HIV-1 group M and the variable units are notable for rapid changes in amino acid sequence length. Increases in gp120 variability result in significantly elevated levels of viral replication, indicating an increase in viral fitness in individuals infected by diverse HIV-1 variants.^[4] Further studies have shown that variability in potential N-linked glycosylation sites (PNGSs) also result in increased viral fitness. PNGSs allow for the binding of long-chain carbohydrates to the high variability regions of gp120, so the authors hypothesize that the number of PNGSs in env might affect the fitness of the virus by providing more or less sensitivity to neutralizing antibodies. The presence of large carbohydrate chains extending from gp120 might obscure possible antibody binding sites.^[5]

The boundaries of the potential to add and eliminate PNGSs are naively explored by growing viral populations following each new infection.^[6] While the transmitting host has developed a neutralizing antibody response to gp120, the newly infected host lacks immune recognition of the virus. Sequence data shows that initial viral variants in an immunologically naïve host have few glycosylation sites and shorter exposed variable loops. This may facilitate viral ability to bind host cell receptors.^[7] As the host immune system develops antibodies against gp120, immune pressures seem to select for increased glycosylation, particularly on the exposed variable loops of gp120.^[8] Consequently, insertions in env, which confer more PNGSs on gp120 may be more tolerated by the virus as higher glycan density promotes the viral ability to evade antibodies and thus promotes higher viral fitness.^[9] In considering how much PNGS density could theoretically change, there may be an upper bound to PNGS number due to its inhibition of gp120 folding, but if the PNGS number decreases substantially, then the virus is too easily detected by neutralizing antibodies.^[6] Therefore, a stabilizing selection balance between low and high glycan densities is likely established. A lower number of bulky glycans improves viral replication efficiency and higher number on the exposed loops aids host immune evasion via disguise.

The relationship between gp120 and neutralizing antibodies is an example of Red Queen evolutionary dynamics. Continuing evolutionary adaptation is required for the viral envelope protein to maintain fitness relative to the continuing evolutionary adaptations of the host immune neutralizing antibodies, and vice-versa, forming a coevolving system.^[9]

[edit] Vaccine target

Since CD4 receptor binding is the most obvious step in HIV infection, gp120 was among the first targets of HIV vaccine research. Efforts to develop HIV vaccines targeting gp120, however, have been hampered by the chemical and structural properties of gp120, which make it difficult for antibodies to bind to it. gp120 can also easily be shed from the surface of the virus and captured by T cells due to its loose binding with gp41. A conserved region in the gp120 glycoprotein that is involved in the metastable attachment of gp120 to CD4 has now been identified and targeting of invariant region has been achieved with a broadly neutralising antibody, b12.^[10]

Research presented at the 17th International AIDS Conference in Mexico City provided the possibility of a new vaccine based on antibodies that hydrolyze or cleave apart the gp120 protein,^[11] rendering it incapable of binding to lymphocytes.^[12] This binding is the first step in the process of HIV infection. The antibody, IgA, is present in all human beings, but its potential for combating HIV was first recognized in patients with lupus, who exhibited both an abnormal resistance to HIV infection and an abnormally high concentration of IgA.^[12] Scientists confirmed that IgA purified from the blood plasma and saliva of HIV-seronegative subjects cleaved gp120 more effectively than the more naturally abundant IgG did, which had little or no effect.^[11] To combat HIV, IgA could be administered in large doses as a drug to people already infected. Researchers have yet to make a vaccine which stimulates the body to increase its own production of IgA.^[12]

NIH research published in Science reports the discovery of antibodies that bind 91% of HIV-1 strains at the CD4bs region of gp120 potentially offering a therapeutic and vaccine strategy. [1]

[edit] Competition

Main article: Entry inhibitors

The protein gp120 is necessary during the initial binding of HIV to its target cell. Consequently, anything which binds to gp120's target can block gp120 from binding to a cell by being physically in the way. Many of these are toxic to the immune system, such as the anti-CD4 monoclonal antibody OKT4.

EGCG, a flavonoid found in green tea, binds to the same CD4 receptor that gp120 binds to, effectively competing for this receptor. Test tube studies suggested that EGCG concentrations as low as 0.2 mmols/L – the concentration of the molecule found in a cup of green tea – temporarily reduced HIV-CD4 cell binding by 40%.^[13] Further research is needed both to confirm that this one-time laboratory experiment can be repeated successfully and to see whether the result has any practical effect. For example, by binding to CD4, the flavonoid might slow the progression of AIDS, but it might also attract an antibody response against the non-human flavonoid that destroys an immune system. One important aspect of EGCG is that, unlike antiretroviral drugs, it can penetrate the blood brain barrier, and may help prevent the onset of AIDS-related dementia.

[edit] HIV dementia

The HIV viral protein gp120 induces apoptosis of neuronal cells. gp120 induces mitochondrial-death proteins like caspases which may influence the upregulation of the death receptor Fas leading to apoptosis of neuronal cells,^[14] gp120 induces oxidative stress in the neuronal cells,^[15] and it is also known to activate STAT1 and induce interleukins IL-6 and IL-8 secretion in neuronal cells.^[16]

[edit] References

^ Kuiken, C., Leitner, T., Foley, B., et al. (2008). "HIV Sequence Compendium", Los Alamos National Laboratory.
^ Zhu P, Winkler H, Chertova E, Taylor KA, Roux KH (November 2008). "Cryoelectron tomography of HIV-1 envelope spikes: further evidence for tripod-like legs". PLoS Pathog. 4 (11): e1000203. doi:10.1371/journal.ppat.1000203. PMC 2577619. PMID 19008954. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2577619.
^ Wyatt, R., Kwong, P., Desjardins, E., Sweet, R., Robinson, J., Hendrickson, W., and Sodroski, J. (1998). "The antigenic structure of the HIV gp120 envelope gycoprotein". Nature 393 (6686): 705–711. doi:10.1038/31514. PMID 9641684.
^ Novitsky, V., Lagakos, S., Herzig, M., Bonney, C., Kebaabetswe, L., Rossenkhan, R., Nkwe, D., Margolin, L., Musonda, R., Moyo, S., Woldegabriel, E., van Widenfelt, E., Mkhema, J., and Essex, M. (2009). "Evolution of proviral gp120 over the first year of HIV-1 subtype C infection". Journal of Virology 383 (1): 47–59. doi:10.1016/j.virol.2008.09.017. PMC 2642736. PMID 18973914. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2642736.
^ Wood, N., Bhattacharya, T., Keele, B.,Giorgi, E., Liu, M., Gaschen, B., Daniels, M., Ferrari, G., Haynes, B., McMichael, A., Shaw, G., Hahn, B., Korber, B., and Seoighe, C. (2009). "HIV evolution in early infection: selection pressures, patterns of insertion and deletion, and the impact of APOBEC". PLOS Pathogens 5: 1–16.
^ ^a ^b Zhang, M., B. Gaschen, W. Blay, B. Foley, N. Haigwood, C. Kuiken, and B. Korber. (2004). "Tracking global patterns of n-linked glycosylation site variation in highly variable viral glycoproteins: hiv, siv, and hcv envelopes and influenza hemagglutinin.". Glycobiology 14: 1229–1246. doi:10.1093/glycob/cwh106. PMID 15175256.
^ Liu Y, Curlin ME, Diem K, Zhao H, Ghosh AK, Zhu H, Woodward AS, Maenza J, Stevens CE, Stekler J, Collier AC, Genowati I, Deng WZioni R, Corey L, Zhu T, Mullins JI (May 2008). "Env length and N-linked glycosylation following transmission of human immunodeficiency virus Type 1 subtype B viruses". Virology 374 (2): 229–33. doi:10.1016/j.virol.2008.01.029. PMC 2441482. PMID 18314154. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2441482.
^ Pantophlet R, Burton DR (2006). "GP120: target for neutralizing HIV-1 antibodies". Annu. Rev. Immunol. 24. doi:10.1146/annurev.immunol.24.021605.090557. PMID 16551265.
^ ^a ^b Frost, S. D. W., T. Wrin, D. M. Smith, S. L. K. Pond, Y. Liu, E. Paxinos, C. Chappey, J. Galovich, J. Beauchaine, C. J. Petropoulos, S. J. Little, and D. D. Richman. (2005). "Neutralizing antibody responses drive the evolution of human immunodeficiency virus type 1 envelope during recent hiv infection.". Proceedings of the National Academy of Sciences of the USA 102: 18514–18519.
^ Zhou T, Xu L, Dey B, et al. (2007). "Structural definition of a conserved neutralization epitope on HIV-1 gp120". Nature 445 (7129): 732–737. doi:10.1038/nature05580. PMC 2584968. PMID 17301785. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2584968.
^ ^a ^b Planque, S., Mitsuda, Y., Taguchi, H., et al. (2007). "Characterization of gp120 Hydrolysis by IgA Antibodies from Humans without HIV Infection". AIDS Research and Human Retroviruses 23 (12): 1541–1554. doi:10.1089/aid.2007.0081. PMID 18160012.
^ ^a ^b ^c Brown, David, "Antibodies May Lead to Protection Against HIV", The Washington Post, 8 August 2008.
^ AIDSmeds.com - Top Stories : Green Tea for HIV? - by Tim Horn
^ Thomas S, Mayer L, Sperber K (2009). "Mitochondria influence Fas expression in gp120-induced apoptosis of neuronal cells". Int. J. Neurosci. 119 (2): 157–65. doi:10.1080/00207450802335537. PMID 19125371.
^ Price TO, Ercal N, Nakaoke R, Banks WA (May 2005). "HIV-1 viral proteins gp120 and Tat induce oxidative stress in brain endothelial cells". Brain Res. 1045 (1-2): 57–63. doi:10.1016/j.brainres.2005.03.031. PMID 15910762.
^ Yang B, Akhter S, Chaudhuri A, Kanmogne GD (March 2009). "HIV-1 gp120 induces cytokine expression, leukocyte adhesion, and transmigration across the blood-brain barrier: modulatory effects of STAT1 signaling". Microvasc. Res. 77 (2): 212–9. doi:10.1016/j.mvr.2008.11.003. PMID 19103208.

[edit] Further reading

Human Immunodeficiency Virus Glycoprotein 120

Vashistha H, Husain M, Kumar D, Singhal PC (2009). "Tubular cell HIV-1 gp120 expression induces caspase 8 activation and apoptosis". Ren Fail 31 (4): 303–12. doi:10.1080/08860220902780101. PMID 19462280.

[edit] External links

[edit] See also

HIV structure and genome

Viral proteins (early and late)

DNA

Herpes simplex	Herpes simplex virus protein vmw65 · HHV capsid portal protein

Hepatitis B	HBsAg · HBcAg (HBeAg) · HBx · Hepatitis B virus DNA polymerase

Epstein-Barr	EBNA-1 · EBNA-2 · EBNA-3 · LMP-1 · LMP-2 · EBER

RNA

Rotavirus	VNPs: NSP1 · NSP2 · NSP4 · NSP5 · NSP6

Influenza	capsid: matrix protein (M1 protein) · viral envelope (M2 protein) glycoprotein: Influenza hemagglutinin · Neuraminidase

Parainfluenza	Parainfluenza hemagglutinin-neuraminidase

Mumps	Mumps hemagglutinin-neuraminidase

Measles	Measles hemagglutinin

RSV	Respiratory syncytial virus G protein

Hepatitis C	VSPs: E1 · E2 VNPs: P7 · NS2 · NS3 · NS4 · NS5

RT

Structure and genome of HIV	VSPs: gag · pol (Integrase, Reverse transcriptase, HIV-1 protease) · env (gp120, gp41) VRAPs: transactivators (Tat, Rev, Vpr) · Nef · Vif · Vpu

Fusion protein

Gag-onc fusion protein

M: VIR

virs(prot)/clss

cutn/syst (hppv/hiva, infl/zost/zoon)/epon

drugJ(dnaa, rnaa, rtva, vacc)

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Envelope glycoprotein GP120

The entry of HIV requires interaction of viral GP120 with P01730 and a chemokine receptor on the cell surface.

Literature references

Kwong PD, Wyatt R, Robinson J, Sweet RW, Sodroski J, Hendrickson WA; , Nature 1998;393:648-659.: Structure of an HIV gp120 envelope glycoprotein in complex with the CD4 receptor and a neutralizing human antibody. PUBMED:9641677

External database links

HOMSTRAD:	GP120
PANDIT:	PF00516
Pseudofam:	PF00516
SCOP:	1gc1
SYSTERS:	GP120

This tab holds annotation information from the InterPro database.

InterPro entry IPR000777

The entry of HIV requires interaction of viral GP120, an envelope glycoprotein with human T-cell surface glycoprotein CD4 and a chemokine receptor on the cell surface. These envelope glycoproteins are found in HIV types 1 and 2, and Simian Immunodeficiency virus (SIV).

Gene Ontology

The mapping between Pfam and Gene Ontology is provided by InterPro. If you use this data please cite InterPro.

Cellular component

viral envelope (GO:0019031)

Domain organisation

Below is a listing of the unique domain organisations or architectures in which this domain is found. More...

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Alignments

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Pfam alignments:	Seed (24) Full (121400) NCBI (101889) Metagenomics
Full length sequences	Full-sequences (121400)

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Curation and family details

This section shows the detailed information about the Pfam family. You can see the definitions of many of the terms in this section in the glossary and a fuller explanation of the scoring system that we use in the scores section of the help pages.

Curation

Seed source:

Pfam-B_44 (release 1.0)

Previous IDs:

none

Type:

Family

Author:

Finn RD

Number in seed:

24

Number in full:

121400

Average length of the domain:

215.90 aa

Average identity of full alignment:

52 %

Average coverage of the sequence by the domain:

78.00 %

HMM information

HMM build commands:

build method: hmmbuild -o /dev/null HMM SEED

search method: hmmsearch -Z 15929002 -E 1000 --cpu 4 HMM pfamseq

Model details:

Parameter	Sequence	Domain
Gathering cut-off	19.9	18.0
Trusted cut-off	19.9	18.0
Noise cut-off	19.8	17.9

Model length:

488

Family (HMM) version:

13

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Species distribution

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Structures

For those sequences which have a structure in the Protein DataBank, we use the mapping between UniProt, PDB and Pfam coordinate systems from the PDBe group, to allow us to map Pfam domains onto UniProt sequences and three-dimensional protein structures. The table below shows the structures on which the GP120 domain has been found. There are 36 instances of this domain found in the PDB. Note that there may be multiple copies of the domain in a single PDB structure, since many structures contain multiple copies of the same protein seqence.

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Family: GP120 (PF00516)

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Summary: Envelope glycoprotein GP120

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Envelope glycoprotein GP120

Contents

[edit] Variability

[edit] Vaccine target

[edit] Competition

[edit] HIV dementia

[edit] References

[edit] Further reading

[edit] External links

[edit] See also

Envelope glycoprotein GP120

Literature references

External database links

InterPro entry IPR000777

Gene Ontology

Domain organisation

Alignments

Viewing

Downloading

View options

Formatting options

Download options

External links

HMM logo

Trees

Curation and family details

Curation

HMM information

Species distribution

Sunburst controls

Weight segments by...

Change the size of the sunburst

Colour assignments

How the sunburst is generated

Colouring and labels

Anomalies in the taxonomy tree

Missing taxonomic levels

Unmapped species names

Sub-species

Too many species/sequences

Tree controls

Annotation

Download tree

Selected sequences

Species trees

Interactive tree

Structures