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pubmed-article:10504397, pubmed-article:11318594, pubmed-article:12396016, pubmed-article:1744579, pubmed-article:1875953, pubmed-article:7507842, pubmed-article:7642209, pubmed-article:7739575, pubmed-article:8245486, pubmed-article:8252810, pubmed-article:9443108, pubmed-article:9780209

Fibronectin, which is present in submandibular saliva, binds to HIV-1 gp120/160 and enhances the interaction of C1q with gp120/160, Free C1q binds to HIV-1 gp120; digestion of the C1q stem portion with collagenase completely eliminates its binding to recombinant gp120, suggesting that the collagen-like stem region of C1q participates in the binding to gp120, HIV-1 gp41 (amino acid residues 561-575, 591-605 and 601-620) binds to complement C1q and activates the C1 complex in a dose- and time-dependent manner, The interaction between C1q and HIV-gp41 is dependent upon the presence of calcium; calcium can not be replaced by larger cations such as strontium, barium, lead or smaller ions such as magnesium and manganese, Three sites (amino acids 526-538, 590-613 and 625-655) of the cell-external part of HIV-1 gp41 bind both HIV-1 gp120 and C1q