Co-operativity between modules within a C3b-binding site of complement receptor type 1

Complement receptor type 1 (CR1) has 30 modules in its extracellular portio n. An understanding of structure-function relationships,Within CR1 is being assembled gradually from studies of overlapping protein fragments. A CRI f ragment corresponding to modules 16 and 17 was expressed recombinantly as a non-glycosylated protein and its stability and unfolding characteristics s tudied using biophysical techniques. The results were compared with data co llected previously on a CR1 fragment encompassing modules 15, 16 and 17 whi ch together constitute a C3b-binding site (Kirkitadze, M.D., Krych, M., Uhr in, D., Dryden, D.T.F., Smith, B.O., Wang, X., Hauhart, R., Atkinson, J.P. and Barlow, P.N. (1999) Biochemistry 38, 7019-7031). Modules within CR1 wer e found to cooperate during unfolding. The folding, stability and flexibili ty of this protein is therefore likely to be a complex function, and not ju st the sum, of contributions from individual modules. (C) 1999 Federation o f European Biochemical Societies.