Modulation of protein's activity in dimensionality restricted spaces

EDUARDO M. CLOP; PEDRO D. CLOP; JULIETA M. SÁNCHEZ; VERÓNICA M. NOLAN; MARIA A. PERILLO

Salta

Congreso; Sociedad Argentina de Biofísica XXXIX; 2010

The reaction confinement to dimensionally restricted spaces such as a percolation matrix or a surface, like in cellular environments, can cause significant effects on reactions mechanism and rate. The accompanying molecular crowding may be affecting the probability of enzyme-substrate collisions due to the excluded volume and the thermodynamic activity of water due to its structuring at surfaces. Monomolecular reactions are not affected by dimensionality restrictions due to their unitary kinetic order. This is a reasonable assumption because, in these cases, dimensionality restrictions are not expected to affect the probability that an isolated molecule exhibits spontaneous cleavage or conformational change. However, dimensionality restrictions have a greater influence in collision probabilities and, hence, in the rate of a bimolecular reaction. A fractal kinetics may arise in restricted reaction conditions when the potential-energy surface that has to be explored during the reaction possesses fractal properties. In those cases, kinetic orders will reflect the fractal dimension of the surface where the reaction is taking place. In both conditions, protein structure and function can also be affected. Under this hypothesis, we studied the structure/activity relationship of two proteins. One of them was an aqueous soluble protein (Beta-Galactosidase) bound to a lipid-water interface and the other one was a membrane-anchored protein (placental alkaline phosphatase) which in natural conditions is immersed in the molecular crowded environment of the cellular glycocalix. In both cases we used Langmuir and Langmuir-Blodgett films as membrane models, with or without a pseudo-glycocalix and evaluated protein conformation and activity. Across-talk between protein and environmental structure was evidenced through kinetics.