UNFOLDING OF BACTERIOPHAGE-P22 TAILSPIKE PROTEIN - ENHANCED THERMAL-STABILITY OF AN N-TERMINAL FUSION MUTANT

The tailspike protein (TSP) of bacteriophage P22 is a homotrimeric mul tifunctional protein responsible for cell attachment and hydrolysis of the Salmonella typhimurium host cell receptor. Despite the folding of TSP involves the formation of thermolabile intermediates, the mature protein is extremely resistant to heat and detergent denaturation, We have analyzed the thermal resistance and unfolding pathway of two muta nt, functional TSPs carrying end-terminal peptide fusions, Whereas the C-terminal fusion has minor effects on the TSP stability, the presenc e of a 23-mer foreign peptide at the N terminus (protein ATSP) results in a significant enhancement of the thermal resistance by retarding t he first transition step of the unfolding process, At 65 degrees C and in 2% SDS, the unfolding rate constant for the transition from the na tive to the unfolding intermediate is 9.3 x 10(-4) s(-1) for ATSP vers us 1.7 x 10(13) s(-1) for wild-type TSP, On the other hand, the electr ophoretic mobility of ATSP intermediates is greatly affected, proving structural modifications induced by the fused peptide, These results s uggest a critical participation of the N-terminal domain in the unfold ing kinetic barriers generated during the TSP denaturation pathway. (C ) 1998 Federation of European Biochemical Societies.