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PROSITE documentation PDOC00119 [for PROSITE entry PS51348]

Alpha-lactalbumin / lysozyme C family signature and profile


α-lactalbumin [1], a milk protein, is the regulatory subunit of lactose synthase. In the mammary gland, α-lactalbumin changes the substrate specificity of galactosyltransferase from N-acetylglucosamine to glucose.

Lysozymes (EC [2] act as bacteriolytic enzymes by hydrolyzing the β(1->4) bonds between N-acetylglucosamine and N-acetylmuramic acid in the peptidoglycan of prokaryotic cell walls. There are at least five different classes of lysozymes [3,4]: C (chicken type), G (goose type), phage-type (T4), fungi (Chalaropsis), and bacterial (Bacillus subtilis) but there are few similarities in the sequences of the different types of lysozymes.

α-lactalbumin and lysozyme C are evolutionary related [5]. Around 35 to 40% of the residues are conserved in both proteins as well as the positions of the four disulfide bonds (see the schematic representation). The pattern for this family of proteins includes three cysteines involved in two of these disulfide bonds (the first cysteine is linked to the third one).

                                  |     **|*******
       |          |                     +--------+         |    |
       |          +----------------------------------------+    |
'C': conserved cysteine involved in a disulfide bond.
'*': position of the pattern.

We also developed a profile that covers the entire α-lactalbumin / lysozyme C.


These proteins belong to family 22 in the classification of glycosyl hydrolases [6,E1].

Last update:

December 2007 / Text revised; profile added.


Technical section

PROSITE methods (with tools and information) covered by this documentation:

LACTALBUMIN_LYSOZYME_2, PS51348; Alpha-lactalbumin / lysozyme C family profile  (MATRIX)

LACTALBUMIN_LYSOZYME_1, PS00128; Alpha-lactalbumin / lysozyme C signature  (PATTERN)


1AuthorsHall L. Campbell P.N.
TitleAlpha-lactalbumin and related proteins: a versatile gene family with an interesting parentage.
SourceEssays Biochem. 22:1-26(1986).
PubMed ID3104032

2SourceConcise Encyclopedia Biochemistry, Second Edition, Walter de Gruyter, Berlin New-York (1988).

3AuthorsWeaver L.H. Grutter M.G. Remington S.J. Gray T.M. Isaacs N.W. Matthews B.W.
SourceJ. Mol. Evol. 21:97-111(1985).

4AuthorsKamei K. Hara S. Ikenaka T. Murao S.
TitleAmino acid sequence of a lysozyme (B-enzyme) from Bacillus subtilis YT-25.
SourceJ. Biochem. 104:832-836(1988).
PubMed ID3148618

5AuthorsNitta K. Sugai S.
TitleThe evolution of lysozyme and alpha-lactalbumin.
SourceEur. J. Biochem. 182:111-118(1989).
PubMed ID2731545

6AuthorsHenrissat B.
TitleA classification of glycosyl hydrolases based on amino acid sequence similarities.
SourceBiochem. J. 280:309-316(1991).
PubMed ID1747104


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