α₂ Integrin I domain–mediated adhesion to SP-A and MBL. (A-B) Binding of the α₂ integrin I domain (100 nM), E318A α₂ integrin I domain mutant (100 nM), and GST (100 nM) to SP-A was measured in a solid-phase binding assay. Binding was determined in the presence of 2 mM MgCl₂, 2 mM MnCl_2, or 1 mM EDTA. (B) GST control was subtracted from experimental data. (C) Binding of the α₂ integrin I domain (100 nM), E318A α₂ integrin I domain mutant (100 nM), and GST (100 nM) to MBL was measured in a solid-phase binding assay. Binding was determined in the presence of 2 mM MgCl₂ plus CaCl₂ or 1 mM EDTA, as indicated. All results are presented as mean ± SEM from triplicate wells of a single experiment and represent 1 of at least 3 experiments demonstrating similar results. In all cases, at least 2 different preparations of purified I domain were used to verify that any results were not unique to a particular protein preparation.