Nitrated SP-A does not enhance adherence of Pneumocystis carinii to alveolar macrophages.
We investigated whether nitration of surfactant apoprotein (SP) A alters its ability to bind to mannose-containing saccharides on Pneumocystis carinii and its potential role in the mediation of P. carinii adherence to alveolar macrophages. Human SP-A was nitrated by incubation with tetranitromethane at pH 8.0 or synthetic peroxynitrite (ONOO-) at pH 7.4, which resulted in significant nitration of tyrosines in its carbohydrate recognition domain [0.63 +/- 0.001 (SE) and 1.25 +/- 0.02 mol nitrotyrosine/mol monomeric SP-A, respectively; n = 3 samples]. Binding of SP-A to P. carinii was calcium dependent and competitively inhibited by alpha-methyl-D-mannopyranoside. Nitration of SP-A by ONOO- or tetranitromethane decreases its binding to P. carinii by increasing its dissociation constant from 7.8 x 10(-9) to 1.6 x 10(-8) or 2.4 x 10(-8) M, respectively, without significantly affecting the number of binding sites (7.1 x 10(6)/P. carinii organisms, assuming that the native molecular mass of oligomeric SP-A is 650 kDa). Furthermore, ONOO--nitrated SP-A failed to mediate the adherence and phagocytosis of P. carinii to rat alveolar macrophages as observed with normal SP-A. Binding of SP-A to rat alveolar macrophages was not altered by nitration. These results indicate that nitration of SP-A interferes with its ability to serve as a ligand for P. carinii adherence to alveolar macrophages at the site of the SP-A moleculeP. carinii interaction.
Zhu
S
S
Department of Anesthesiology, University of Alabama at Birmingham, Birmingham, Alabama 35233, USA.
Kachel
D L
DL
Martin
W J
WJ
Matalon
S
S
D000818:Animals; D004533:Egtazic Acid / Q000494:pharmacology; D006801:Humans; D016676:Macrophages, Alveolar / Q000378:metabolism / Q000502:physiology*; D009566:Nitrates / Q000378:metabolism*; D010587:Phagocytosis / Q000187:drug effects; D011010:Pneumocystis / Q000187:drug effects* / Q000378:metabolism / Q000502:physiology*; D011510:Proteolipids / Q000378:metabolism* / Q000494:pharmacology*; D037662:Pulmonary Surfactant-Associated Protein A; D037661:Pulmonary Surfactant-Associated Proteins; D011663:Pulmonary Surfactants / Q000378:metabolism* / Q000494:pharmacology*; D051381:Rats; D011917:Rats, Inbred Lew
D009566:Nitrates; D011510:Proteolipids; D037662:Pulmonary Surfactant-Associated Protein A; D037661:Pulmonary Surfactant-Associated Proteins; D011663:Pulmonary Surfactants; C039642:peroxynitric acid; D004533:Egtazic Acid