Characteristic noise features in light transmission across membrane protein undergoing photocycle

摘要

We demonstrate a technique based on noise measurements which can be utilizedto study dynamical processes in protein assembly. Direct visualization ofdynamics in membrane protein system such as bacteriorhodopsin (bR) uponphotostimulation are quite challenging. bR represents a model system where thestimulus-triggered structural dynamics and biological functions are directlycorrelated. Our method utilizes a pump-probe near field microscopy method inthe transmission mode and involves analyzing the transmittance fluctuationsfrom a finite size of molecular assembly. Probability density distributionsindicating the effects of finite size and statistical correlations appear as acharacteristic frequency distribution in the noise spectra of bR whose origincan be traced to photocycle kinetics. Valuable insight into the molecularprocesses were obtained from the noise studies of bR and its mutant D96N as afunction of external parameters such as temperature, humidity or presence of anadditional pump source.