Summary

C-type lysozyme/alpha-lactalbumin family

Alpha-lactalbumin is the regulatory subunit of lactose synthase, changing the substrate specificity of galactosyltransferase from N-acetylglucosamine to glucose. C-type lysozymes are secreted bacteriolytic enzymes that cleave the peptidoglycan of bacterial cell walls. Structure is a multi-domain, mixed alpha and beta fold, containing four conserved disulfide bonds.

InterPro entry IPR001916

O-Glycosyl hydrolases are a widespread group of enzymes that hydrolyse the glycosidic bond between two or more carbohydrates, or between a carbohydrate and a non-carbohydrate moiety. A classification system for glycosyl hydrolases, based on sequence similarity, has led to the definition of 85 different families PUBMED:7624375, PUBMED:8535779, PUBMED:. This classification is available on the CAZy (CArbohydrate-Active EnZymes) web site PUBMED:. Because the fold of proteins is better conserved than their sequences, some of the families can be grouped in clans.

Glycoside hydrolase family 22 comprises enzymes with two known activities; lysozyme type C () and alpha-lactalbumins. Asp and/or the carbonyl oxygen of the C-2 acetamido group of the substrate acts as the catalytic nucleophile/base.

Alpha-lactalbumin PUBMED:6715332, PUBMED:3104032 is a milk protein that acts as the regulatory subunit of lactose synthetase, acting to promote the conversion of galactosyltransferase to lactose synthase, which is essential for milk production. In the mammary gland, alpha-lactalbumin changes the substrate specificity of galactosyltransferase from N-acetylglucosamine to glucose.

Lysozymes () act as bacteriolytic enzymes by hydrolyzing the beta(1->4) bonds between N-acetylglucosamine and N-acetylmuramic acid in the peptidoglycan of prokaryotic cell walls. It has also been recruited for a digestive role in certain ruminants and colobine monkeys PUBMED:2738070. There are at least five different classes of lysozymes PUBMED:3148618: C (chicken type), G (goose type), phage-type (T4), fungi (Chalaropsis), and bacterial (Bacillus subtilis). There are few similarities in the sequences of the different types of lysozymes.

Lysozyme type C and alpha-lactalbumin are similar both in terms of primary sequence and structure, and probably evolved from a common ancestral protein PUBMED:2731545. Around 35 to 40% of the residues are conserved in both proteins as well as the positions of the four disulphide bonds. There is, however, no similarity in function. Another significant difference between the two enzymes is that all lactalbumins have the ability to bind calcium PUBMED:3785375, while this property is restricted to only a few lysozymes PUBMED:3666156.

The binding site was deduced using high resolution X-ray structure analysis and was shown to consist of three aspartic acid residues. It was first suggested that calcium bound to lactalbumin stabilised the structure, but recently it has been claimed that calcium controls the release of lactalbumin from the golgi membrane and that the pattern of ion binding may also affect the catalytic properties of the lactose synthetase complex.

Clan

This family is a member of clan Lysozyme (CL0037), which contains the following 10 members:

DUF847 Glucosaminidase Glyco_hydro_19 Glyco_hydro_46 Lys Phage_lysozyme REGB_T4 SLT TraH_2 Transglycosylas

External database links

CAZY:	GH_22
HOMSTRAD:	ghf22
PANDIT:	PF00062
PRINTS:	PR00135
PROSITE:	PDOC00119
SCOP:	1lzb
SYSTERS:	Lys

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

There are various ways to view or download the sequence alignments that we store. You can use a sequence viewer to look at either the seed or full alignment for the family, or you can look at a plain text version of the sequence in a variety of different formats. More...

View options

Alignment:	Seed (21) Full (693) NCBI (1756) Metagenomics (9)
Viewer:

Formatting options

Alignment:	Seed (21) Full (693)
Format:
Order:	Tree Alphabetical
Sequence:	Inserts lower case All upper case
Gaps:
Download/view:	Download View

Download options

Very large alignments can often cause problems for the formatting tool above. If you find that downloading or viewing a large alignment is problematic, you can also download a gzip-compressed, Stockholm-format file containing the seed or full alignment for this family.

You can also download a FASTA format file containing the full-length sequences for all sequences in the full alignment.

The main seed and full alignments are generated using sequences from the UniProt sequence database. However, we also generate alignments using sequences from the NCBI sequence database and the "metaseq" metagenomics dataset.

You can view alignments from these two additional datasets using the form above, or you can download alignments of NCBI or metagenomics sequences, as gzip-compressed files.

Pfam alignments:	Seed (21) Full (693) NCBI (1756) Metagenomics (9)
Full length sequences	Full-sequences (693)

External links

MyHits provides a collection of tools to handle multiple sequence alignments. For example, one can refine a seed alignment (sequence addition or removal, re-alignment or manual edition) and then search databases for remote homologs using HMMER2.

HMM logo

HMM logos is one way of visualising profile HMMs. Logos provide a quick overview of the properties of an HMM in a graphical form. You can see a more detailed description of HMM logos and find out how you can interpret them here. More...

Trees

This page displays the phylogenetic tree for this family. We use FastTree to calculate neighbour join trees with a local bootstrap based on 100 resamples (shown next to the tree nodes). FastTree calculates approximately-maximum-likelihood phylogenetic trees from our seed or full alignments.

Note: You can also download the data files for the seed, full, NCBI or metagenomics trees.

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:

Overington and HMM_iterative_training

Previous IDs:

lys;

Type:

Domain

Author:

Eddy SR

Number in seed:

21

Number in full:

693

Average length of the domain:

108.10 aa

Average identity of full alignment:

38 %

Average coverage of the sequence by the domain:

49.47 %

HMM information

HMM build commands:

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

search method: hmmsearch -Z 9421015 -E 1000 HMM pfamseq

Model details:

Parameter	Sequence	Domain
Gathering cut-off	20.9	20.9
Trusted cut-off	21.0	21.0
Noise cut-off	20.8	20.7

Model length:

125

Family (HMM) version:

13

Download:

download the raw HMM for this family

Species distribution

Tree controls

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The tree shows the occurrence of this domain across different species. More...

Species trees

We show the species tree in one of two ways. For smaller trees we try to show an interactive representation, which allows you to select specific nodes in the tree and view them as an alignment or as a set of Pfam domain graphics.

Unfortunately we have found that there are problems viewing the interactive tree when the it becomes larger than a certain limit. Furthermore, we have found that Internet Explorer can become unresponsive when viewing some trees, regardless of their size. We therefore show a text representation of the species tree when the size is above a certain limit or if you are using Internet Explorer to view the site.

If you are using IE you can still load the interactive tree by clicking the "Generate interactive tree" button, but please be aware of the potential problems that the interactive species tree can cause.

Interactive tree

For all of the domain matches in a full alignment, we count the number that are found on all sequences in the alignment. This total is shown in the purple box.

We also count the number of unique sequences on which each domain is found, which is shown in green. Note that a domain may appear multiple times on the same sequence, leading to the difference between these two numbers.

Finally, we group sequences from the same organism according to the NCBI code that is assigned by UniProt, allowing us to count the number of distinct sequences on which the domain is found. This value is shown in the pink boxes.

We use the NCBI species tree to group organisms according to their taxonomy and this forms the structure of the displayed tree. Note that in some cases the trees are too large (have too many nodes) to allow us to build an interactive tree, but in most cases you can still view the tree in a plain text, non-interactive representation. Those species which are represented in the seed alignment for this domain are highlighted.

You can use the tree controls to manipulate how the interactive tree is displayed:

show/hide the summary boxes
highlight species that are represented in the seed alignment
expand/collapse the tree or expand it to a given depth
select a sub-tree or a set of species within the tree and view them graphically or as an alignment
save a plain text representation of the tree

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Interactions

There are 4 interactions for this family. More...

Lys V-set Galactosyl_T_2 Ivy

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 MSD 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 Lys domain has been found.

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Family: Lys (PF00062)

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