Molecular recognition in biological systems'

We have prepared recombinant CD14 and a CD14 fragment consisting of its first 152 residues. This is the first report of the expression of CD14 in a yeast or bacterial system. Both rCD14s were able to bind lipopolysaccharides (LPS). On the basis of CD and fluorescence spectra taking into account that CD14 contains 10 leucine-rech repeats we hypothesize that CD14 contains a mixture of ?- and ?-type structures. We proposed the model for complex between LPS or its active moiety lipid A and polymyxins B and E (peptides neutralizing LPS toxicity) on the basis of NMR and molecular modeling studies. Proposed binding mode breaks the supramolecular structure of LPS connected with its toxicity. The model should contribute to the understanding of entropy-driven PmB-lipid A binding at the molecular level and assist the design of inhibotors of endotoxic activity. Using biophysical (UV, CD, NMR) and biochemical methods we have demonstrated that stefin A forms dimers under denaturating conditions. The dimer is a folded and structured protein although it no more inhibits cysteine proteases. The formation of stefin dimers might, besides representing a model for conformational transitions in dimerization of small single domain proteins, also have physiological relevance for the regulation of its ability to inhibit proteases and for its incorporation into polymerized cell envelope.