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1386  structures 280  species 0  interactions 1733  sequences 36  architectures

Family: Lys (PF00062)

Summary: C-type lysozyme/alpha-lactalbumin family

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This is the Wikipedia entry entitled "Glycoside hydrolase family 22". More...

Glycoside hydrolase family 22 Edit Wikipedia article

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C-type lysozyme/alpha-lactalbumin family Provide feedback

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.

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External database links

This tab holds annotation information from the InterPro database.

InterPro entry IPR001916

O-Glycosyl hydrolases ( EC ) 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 ]. This classification is available on the CAZy (CArbohydrate-Active EnZymes) website.

Glycoside hydrolase family 22 CAZY comprises enzymes with two known activities; lysozyme type C ( EC ) (also known as 1, 4-beta-N-acetylmuramidase or LYZ) and alpha-lactalbumins (also known as lactose synthase B protein or LA). 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 ( EC ) 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.

Sperm acrosome membrane-associated protein 3 (SPACA3) is involved in fertilization, probably during the sperm-egg membrane fusion, but despite being homologous to lysosome has no detectable bacteriolytic activity [ PUBMED:12606493 ].

Domain organisation

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Pfam Clan

This family is a member of clan Lysozyme (CL0037), which has the following description:

Barley chitinase, bacterial chitosanase, and lysozymes from phage and animals all hydrolyse related polysaccharides. The proteins little amino-acid similarity, but have a structurally invariant core consisting of two helices and a three-stranded beta-sheet which form the substrate-binding and catalytic cleft [1].

The clan contains the following 21 members:

Destabilase DUF3218 Glucosaminidase Glyco_hydro_108 Glyco_hydro_19 Glyco_hydro_46 Glyco_hydro_80 Lys Lysozyme_like Peptidase_U40 Pesticin Phage_lysozyme Phage_lysozyme2 SLT SLT_2 SLT_3 SLT_4 TraH_2 Transgly Transglycosylas Utp11


We store a range of different sequence alignments for families. As well as the seed alignment from which the family is built, we provide the full alignment, generated by searching the sequence database (reference proteomes) using the family HMM. We also generate alignments using four representative proteomes (RP) sets and the UniProtKB sequence database. More...

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

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This page displays the phylogenetic tree for this family's seed alignment. 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 alignment.

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Curation and family details

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Seed source: Overington and HMM_iterative_training
Previous IDs: lys;
Type: Domain
Sequence Ontology: SO:0000417
Author: Eddy SR
Number in seed: 12
Number in full: 1733
Average length of the domain: 114.80 aa
Average identity of full alignment: 36 %
Average coverage of the sequence by the domain: 65.69 %

HMM information View help on HMM parameters

HMM build commands:
build method: hmmbuild -o /dev/null HMM SEED
search method: hmmsearch -Z 57096847 -E 1000 --cpu 4 HMM pfamseq
Model details:
Parameter Sequence Domain
Gathering cut-off 20.9 20.9
Trusted cut-off 20.9 20.9
Noise cut-off 20.8 20.8
Model length: 123
Family (HMM) version: 22
Download: download the raw HMM for this family

Species distribution

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Archea Archea Eukaryota Eukaryota
Bacteria Bacteria Other sequences Other sequences
Viruses Viruses Unclassified Unclassified
Viroids Viroids Unclassified sequence Unclassified sequence


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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 Lys domain has been found. There are 1386 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 sequence.

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