Stability analysis of the bacteriophage φKMV lysin gp36C and its putative role during infection

The kinetic, thermodynamic and structural stability of gp36C, the virion-associated peptidoglycan hydrolase domain of bacteriophage phi KMV, is analyzed. Recombinant gp36C is highly thermoresistant (k = 0.595 h(-1) at 95 degrees C), but not thermostable (T-m = 50.2 degrees C, Delta H-cal = 6.86 x 10(4) cal mol(-1)). However, aggregation influences kinetic stability in an unusual manner since aggregation is more pronounced at 55 degrees C than at higher temperatures. Furthermore, gp36C reversibly unfolds in a two-state endothermic transition, and circular dichroism analysis shows that gp36C almost completely refolds after a 3-h heat treatment at 85 degrees C. These properties are in agreement with gp36C being part of the extensible tail which is ejected in an unfolded state during phage infection.