We characterized the structural forms of the human immunodeficiency virus env-encoded proteins with a panel of monoclonal and polyclonal antibodies. Western blot (immunoblot) assays with antibodies specific for gp4l invariably recognized a major component of 160 kilodaltons and a less intense component of 120 kilodaltons in viral lysates. We demonstrated that these species are noncovalently associated tetramers and trimers of gp4l which represent the native form of this protein in virions. These complexes were stable when boiled in the presence of low concentrations of sodium dodecyl sulfate but were dissociated to gp4l monomers at high sodium dodecyl sulfate concentrations. Moreover, two human monoclonal antibodies preferentially recognized the oligomeric complexes over monomeric gp4l in Western blots, indicating the presence of epitopes recognized by the human immune system on the gp4l multimers which are not efficiently expressed by the dissociated monomers. The demonstration of the existence of multimeric env complexes and the enhanced and altered antigenicity of such multimers may be relevant to the design of subunit and recombinant human immunodeficiency virus env vaccines.

Plasminogen (PC), urokinase-type plasminogen activator (u-PA) and tissue-type PA (t-PA) are the main molecules involved in fibrinolysis and in many other physiological and pathological processes. In the present study we report that human t-PA, purified from human melanoma cells, and PG, purified from human plasma, both contain P-Tyr residues, as revealed by immunoblotting analyses with monoclonal anti-P-Tyr antibodies. In addition HPLC amino acid analysis of acid-hydrolyzed t-PA, PG and u-PA, shows that: (i) P-Ser and P-Tyr residues are present in t-PA; (ii) P-Thr and P-Tyr are present in PG; (iii) P-Ser, P-Thr and P-Tyr are present in u-PA. The utilization of monoclonal anti-P-Ser and anti-P-Thr antibodies in immunoblotting experiments has confirmed these data which indicate that phosphorylation is a common feature of PAS and of PG.

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