SAPOSIN-LIKE PROTEINS IN ANTI-INFECTIOUS IMMUNE RESPONSE

Abstract

Abstract. Besides the multiple hydrolytic enzymes, lysosomes are equipped with proteins apt to activate sphyngo-lipids — saposins (SAP). SAP belong to a broad and diverse family of moderate-size (~80 AA) saposin-like proteins (SAPLIP) containing specific domains with three disulfid e bonds bridging six cysteine residues. The diversity of SAPLIPS is likely explained by their involvement in distinct phases of engulfed bacteria digesting. Functionally similar SAPLIP were identified in a wide range of species — from amoeba to mammals, including humans. Saposins per se form a subfamily with six members: saposins A-D and the protein GM2 which possesses activatory functions. SAP do not have enzymatic activity, are heat-stable and protease resistant. The major in vivo function of SAP is released via participation in sphyngolipid catabolism and membrane digestion. In addition, complex association of SAP with membrane bi-layer and CD1 glycolipids is essential for loading lipid antigens onto antigen-presenting CD1 molecules for subsequent activation of lipid-specific T-cells. Of particular interest is participation of SAP in cross-presentation of bacterial antigens to CD8+ T-cells. A broad spectrum of SAP and SAPLIP involvement in the reactions of innate and adaptive immunity indicates their evolutionary conserved role in host defense.

Keywords

• saposins
• saposin-like proteins
• immunity