Scavenger receptor-mediated recognition of maleyl bovine plasma albumin and the demaleylated protein in human monocyte macrophages.

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Abstract
Maleyl bovine plasma albumin competed on an equimolar basis with malondialdehyde low density lipoprotein (LDL) in suppressing the lysosomal hydrolysis of 125I-labeled malondialdehyde LDL mediated by the scavenger receptor of human monocyte macrophages. Maleyl bovine plasma albumin, in which 94% of the amino groups were modfied, exhibited an anodic mobility in agarose electrophoresis 1.7 times that of the native protein. Incubation of maleyl bovine plasma albumin at pH 3.5 regenerated the free amino groups and restored the protein to the same electrophoretic mobility as native hydrolysis of 125I-labeled malondialdehyde LDL and > 80% of 125I-labeled maleyl bovine plasma albumin. The ability of the demaleylated protein to compete was abolished after treatment with guanidine hydrochloride. Although ligands recognized by the scavenger receptor typically are anionic, addition of new negative charge achieved by maleylation, rather than directly forming the receptor binding sites(s), induces conformational changes in albumin as a prerequisite to expression of the recognition domain(s). The altered conformation of the modified protein apparently persists after removal of the maleyl groups. The primary sequence of albumin, rather than addition of new negative charge, provides the recognition determinant(s) essential for interaction of maleyl bovine plasma abumin with the scavenger receptor.