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 3.2.1.17) [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] and form family
22 in the classification of glycosyl hydrolases [6,E1]. 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).
+-------+
| **|*******
xxCxxxxxxxxxxCxxxxxxxxxxxxxxxCxxxxxCxCxxxxxxCxxxxxxxxxCxxxCxx
| | +--------+ | |
| +----------------------------------------+ |
+--------------------------------------------------------+
'C': conserved cysteine involved in a disulfide bond.
'*': position of the pattern.
We also developed a profile that covers the entire glycosyl hydrolases family
22 domain.
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