Primary structures of two hemagglutinins from the marine red alga, Hypnea japonica

As the first examples among marine algal hemagglutinins, the primary struct ures of two hemagglutinins, named hypnin A-1 and A-2, from the red alga Hyp nea japonica, were determined by Edman degradation. Both hemagglutinins wer e single-chain polypeptides composed of 90 amino acid residues including fo ur half-cystines, all of which were involved in two intrachain disulfide bo nds, Cys(5)-Cys(62) and Cys(12)-Cys(89). Hypnin A-1 and A-2 had calculated molecular masses of 9146.7 and 9109.7 Da which coincided with determined va lues, 9148 and 9109 Da, by electrospray ionization-mass spectrometry, respe ctively. Both hemagglutinins only differed from each other at three positio ns; Pro(19), Arg(31) and Phe(52) of hypnin A-1 as compared with Leu(19), Se r(31), and Tyr(52) of hypnin A-2. Approximately 43% of total residual numbe rs consisted of three kinds of amino acids: serine, glycine and proline. Th e hemagglutination activities were lost by reduction and alkylation of the disulfide bonds. The nature of the small-sized polypeptides, including disu lfide bonds, may contribute to the extreme thermostability of the hemagglut inins. Sequence having overall similarity to hypnin A-1 or A-2 was not dete cted in databases. Unexpectedly, however, hypnins contained a motif similar to the alignment of the C-terminal conserved amino acids within carbohydra te recognition domains of C-type animal lectins. Furthermore, interestingly , the hemagglutination activities were inhibited by a protein, phospholipas e A-2 besides some glycoproteins, suggesting that hypnins may possess both a protein-recognition site(s) and a carbohydrate-recognition site(s). (C) 2 000 Elsevier Science B.V. All rights reserved.