Prostate a-Protein COMPLETE AMINO ACID SEQUENCE OF THE COMPONENT THAT INHIBITS NUCLEAR RETENTION OF THE ANDROGEN-RECEPTOR COMPLEX*

The amino acid sequence of Component I of a-protein, a glutamic acid-rich protein, is presented. Component I is a single chain polypeptide which consists of 88 amino acid residues with a molecular weight of 10,191. Component I has the amino acid composition LysS, His, Argz, Cys3, Asps, Asn,, Thr,, Ser4, G1uI3, Gln3, ho3, Gly,, Alas, Val,, Met4, Ile4, Leus, Tyr~, Phe3, Trp, with serine and asparagine as NH2- and COOH-terminal amino acids, respectively. Automated sequence analysis of the whole protein, as well as characterization of the peptides obtained from trypsin, chymotrypsin, and staphylococcal protease digestion and cyanogen bromide treatment, led to the elucidation of the complete primary structure of this protein.

The amino acid sequence of Component I of a-protein, a glutamic acid-rich protein, is presented. Component I is a single chain polypeptide which consists of 88 amino acid residues with a molecular weight of 10,191. Component I has the amino acid composition LysS, His, Argz, Cys3, Asps, Asn,, Thr,, Ser4, G1uI3, Gln3, ho3, Gly,, Alas, Val,, Met4, Ile4, Leus, Tyr~, Phe3, Trp, with serine and asparagine as NH2-and COOH-terminal amino acids, respectively. Automated sequence analysis of the whole protein, as well as characterization of the peptides obtained from trypsin, chymotrypsin, and staphylococcal protease digestion and cyanogen bromide treatment, led to the elucidation of the complete primary structure of this protein.

NH2-Ser-Gln-~e-CysClu-Leu-Val-Ala-His-Glu-Thr-~e~er-Phe-Leu-Met-Lys-Ser-GluClu-Glu-Leu-30
40 a-Protein was fist identified as a nonreceptor steroid-binding protein in the rat ventral prostate which could, in uitro, inhibit the association of an androgen-receptor complex with nuclear chromatin (1). The inhibitory effect is not related to the steroid-binding capability of a-protein (2). In the accompanying paper (3), we showed that a-protein has two subunits (A and B), each of which consists of two polypeptide components. Component I in subunit A was identified as the active polypeptide that can interfere with the retention of the andro- cy-Protein and its Component I were isolated from the ventral prostate of Sprague-Dawley rats by the procedure described in the accompanying paper (3).

DISCUSSION
In the accompanying paper (3), we presented evidence that the inhibition of chromatin retention of the prostatic androgen-receptor complex by a-protein is due to Component I. Although this component is a glutamic acid-rich polypeptide, the inhibitory activity may not be dependent on the high acidic amino acid content alone, since Component I11 and subunit B of a-protein, which have acidic amino acid contents similar to that of Component I, are not active.
Most of the glutamic acid and lysine residues in Component I are localized in the NHz-terminal half, whereas all aspartic acid residues and nearly all of the aromatic acids are in the COOH-terminal half of the protein. Whether these features are important in the inhibition of the Chromatin retention of the receptor complex is not clear. It is possible that the inhibitory activity is due to a small oligopeptide stretch in Component I and that it does not require a complex structure.
Although the biological importance of a-protein in the rat print are: CNBr, cyanogen bromide peptides; C, a-chymotryptic peptides; SP, peptides obtained by digestion with staphylococcal protease; OT, tryptic peptides obtained from the whole oxidized component I; CiT, tryptic peptides obtained from the whole S-carboxymethylated, citraconylated Component I.
ventral prostate is not clear, it is known that this secretory protein can interact with several cellular components, such as cholesterol, androgens, and polyamines, which can play major roles in prostate growth. A thorough knowledge of the molecular assembly of a-protein may provide a better understanding of these protein-ligand interactions and of the mechanism by which this complex protein is synthesized and secreted.