Covalent structure of apolipoprotein A-II from Macaca mulatta serum high-density lipoproteins

Abstract

The covalent structure of apolipoprotein A-II, isolated from the serum high-density lipoprotein of a single male rhesus monkey (Macaca mulatta), was determined. The amino acid sequence of this 77-residue polypeptide is: < Glu-Ala-Glu-Glu-Pro5-Ser-Val-Glu-Ser-Leu10-Val-Ser-Gln-Tyr-Phe15-Gln-Thr-Val-Thr-Asp20-Tyr-Gly-Lys-Asp-Leu25-Met-Glu-Lys-Val-Lys30-Ser-Pro-Glu-Leu-Gln35-Ala-Gln-Ala-Lys-Ala40-Tyr-Phe-Glu-Lys-Ser45-Lys-Glu-Gln-Leu-Thr50-Pro-Leu-Val-Lys-Lys55-Ala-Gly-Thr-Asp-Leu60-Val-Asn-PheLeu-Ser65-Tyr-Phe-Val-Glu-Leu70-Arg-Thr-Gln-Pro-Ala75-Thr-Gln-COOH. A comparison of this structure to that of monomeric form of human apolipoprotein A-II reveals a high degree of homology except for 6 conservative amino acid replacements (positions 3, 6, 40, 53, 59 and 71). Of particular structural significance is the replacement of cysteine by serine in position 6. This explains why Rhesus A-II exists in monomeric form, contrary to the established dimeric nature of the human protein.