Signification fonctionnelle des séquences signal : leur rôle dans le transfert des lactoprotéines à travers les membranes du réticulum endoplasmique

Abstract

The mammary gland of the ruminant synthesizes and secretes six major proteins: 4 caseins (alpha S1, alpha S2, beta and kappa), alpha-lactalbumin and beta-lactoglobulin. The information which determines the translocation of these proteins across the endoplasmic reticulum membrane resides in their transient amino terminal sequences, the so-called much less than signal sequences much greater than. These sequences are cleaved by a specific membrane protease during the transfer of nascent polypeptide chains to the lumen of microsomal vesicles. The signal sequences of the various lactoproteins share common features (high hydrophobicity and clustered hydrophobic residues) with other secretory proteins but differ significantly in both length and primary structure. The signal sequences of the 3 much less than calcium sensitive much greater than caseins (alpha S1, alpha S2 and beta) show a high degree of homology, suggesting that they derive from a common ancestor. The study of lactoprotein signal sequences from various mammalian species revealed that the primary structures of the short-lived amino terminal sequences have been well conserved in the course of evolution.