Loops within the CD11c I domain critical for specific recognition of fibrinogen.
The I domains of CD11 are responsible for the binding of ligands and have a unique structure with 6-7 alpha helices and 6 beta sheets with interconnecting loops. To determine loops recognizing fibrinogen in CD11c I domain, five oligopeptides corresponding to CD11c loops were used to prevent fibrinogen binding to isolated CD11c I domain. The results of the inhibition experiment indicated that all of the loops except the one between E-beta sheet and 6-alpha helix were involved in the binding to fibrinogen. The peptide beta D alpha 5 and alpha 3 alpha 4 showed higher inhibitory activity than others, and the combination of four peptides blocked fibrinogen binding to the I domain completely. These peptides (beta A alpha 1, alpha 3 alpha 4, beta D alpha 5 and beta F alpha 7) could block THP-1 cell binding to fibrinogen coated surface as well. Alanine substitution of amino acids on the I domain such as Y249A and Q201A (which are on the loops beta D-alpha 5 and alpha 3-alpha 4 respectively) abolished fibrinogen binding, while mutation on the loop beta E-alpha 6 (Q273A) had no effect on fibrinogen binding. Taken together, the results from this study suggest that the loops on the top of CD11c I domain such as loop beta A-alpha 1, alpha 3-alpha 4, beta D-alpha 5 and beta F-alpha 7 are involved in fibrinogen binding, and two loops (alpha 3-alpha 4 and beta D-alpha 5) are more important than others for the recognition of fibrinogen.
Choi
Jeungsook
J
Division of Science Education, Kangwon National University, Choonchun, Kangwon 200-701, Korea.
Nham
Sang-Uk
SU
D000595:Amino Acid Sequence; D005340:Fibrinogen / Q000378:metabolism*; D016167:Integrin alphaXbeta2 / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D011485:Protein Binding; D017433:Protein Structure, Secondary; D011993:Recombinant Fusion Proteins / Q000378:metabolism
D016167:Integrin alphaXbeta2; D011993:Recombinant Fusion Proteins; D005340:Fibrinogen