Caltrin-like proteins from human seminal plasma. Purification and sequence of a 15 kDa molecule

ANAHí FRANCHI; CARLOS E. CORONEL

Córdoba, Argentina.

Congreso; XIII Jornadas Científicas de la Sociedad de Biología de Córdoba; 2001

Sociedad de Biología de Córdoba

Human seminal plasma (hSP) has two proteins of 34 and 15 kDa that cross-rsact with anti-caltrin (calcrum transporit inhibrtor) ll antibodies. They bind to the acrosomal region of ejaculated sperm, as demonstrated in several species. To study the molecular and functional properties, purification techniques including ammonium sulfate fractionation, exclusion and ion-exchange chromatography, and HPLC were used. Both proteins were partially purified by two cycles of chromatography on Sephadex-G 50 SF. The pI of the small fraction (5.8, estimated by IEF), allowed to separate it by anion exchange together with a protein of 10 kDa. This contaminant was removed by HPLC using an Ultraspherogel Sec 2000 column and both proteins were sequenced. The first 35 residues sequence of the 15 kDa protein showed homology with those of b-inhibin and PSP94 (prostatic secretory protein 94), and the Ser21-Asp55 fragment of the â-MSP (â-microseminoprotein) precursor, from hSP (Kamada et al., BBActa 1388:101, 1998). All three proteins have the same polypeptide chain but the functional role of PSP94 and â-MSP is unknown. The first 30 residues of the 10 kDa protein, showed homology with the precursor of â-2 microglobulin, a component of the major histocompatibility complex. This protein was purified from rat seminal secretion in our laboratory. The cross-reaction with anticaltrin antibodies, and the specific binding to the sperm acrosomal region suggest that the 15 kDa protein could be a molecular form of caltrin.