Spectral dynamics in the B800 band of LH2 from Rhodospirillum molischianum: a single-molecule study

Clemens Hofmann,Hartmut Michel,Jürgen Köhler,Thijs J Aartsma

doi:10.1088/1367-2630/6/1/008

Clemens Hofmann, Hartmut Michel + Show 2 more

Open Access

https://doi.org/10.1088/1367-2630/6/1/008

Copy DOI

Abstract

The BChl a absorptions in the B800 spectrum of individual LH2 complexes from Rhodospirillum molischianum show sudden, reversible spectral jumps between a finite number of spectral positions. From our data, we conclude that these fluctuations result from conformational changes of the protein backbone in close vicinity of the chromophores which provides a sensitive tool to monitor local modulations of the pigment–protein interaction.

Highlights

Since the beginning of single-molecule spectroscopy in the late 1980s [1, 2], the field has undergone breathtaking progress; in particular, the application of single-molecule detection techniques to biology and biochemistry has led to a revolution in these disciplines
Both spectra are in good agreement and consist of two broad bands at 12 500 cm−1 (800 nm) and at 11 800 cm−1 ( ≈ 850 nm), each featuring a linewidth of about 300 cm−1 (FWHM)
The B850 is dominated by a few broad bands which reflect the exciton character of the involved electronic excitations, whereas the B800 band consists of several narrow lines which correspond to excitations that are localized on individual BChl a molecules [20, 21]

Summary

Introduction

Since the beginning of single-molecule spectroscopy in the late 1980s [1, 2], the field has undergone breathtaking progress; in particular, the application of single-molecule detection techniques to biology and biochemistry has led to a revolution in these disciplines. The lowtemperature approach allows to study single molecules over a very long observation period because photobleaching effects of the probe molecules, usually limiting the observation time to some tens of seconds under ambient conditions, are negligible This offers the opportunity to determine the electronic eigenstates of an individual system, i.e. to perform single-molecule spectroscopy rather than single-molecule detection and to apply many experimental techniques from the highly developed toolbox of spectroscopy to single objects [9]–[14]. We report about the spectroscopy of individual pigment–protein complexes from a purple bacterium—Rhodospirillum molischianum These bacteria absorb sunlight by a network of antenna pigment proteins and transfer the excitation energy efficiently to the photochemical reaction centre (RC), where a charge separation takes place, providing the free energy for subsequent chemical reactions. Owing to the relative weak intermolecular interaction between the B800 BChl a molecules, these are suited to act as reporters of their local environment providing information about conformational changes of the protein scaffold

Experimental

Experimental results

Discussion