PARENT SESSION
Posters P3A Bacteriochlorophyll based antenna systems. Abstracts (219-238)

H-bonding in a model bacteriochlorophyll binding site drives assembly of light harvesting complex. Lee Gyan Kwa¹, Adela Garcia-Martin¹, Attila Vegh², Brigitte Strohmann¹, Neil Hunter³, Bruno Robert⁴, Hugo Scheer¹, Paula Braun^*,1, ¹ Department Biologie I der Universität, Botanik, München, Germany² Institute of Biophysics and Radiation Biology, Semmelweis University, Faculty of Medicine, Budapest, Hungary³ Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield, United Kingdom⁴ Section de Biophysique des Fonctions Membranaires, DBJC/CEA and URA CNRS 2096, Saclay, Gif sur Yvette Cedex, France

ABSTRACT- The contribution of intramembrane H-bonding at the interface between polypeptide and cofactor is explored in the native lipid environment by use of model bacteriochlorophyll-proteins. In the peripheral antenna complex, LH2, large portions of the helices, which make up the dimeric bacteriochlorophyll binding site, are replaced by simplified, alternating alanine leucine stretches. Replacement of either one of the two helices with the helices containing the model sequence at a time, results in the assembly of complexes with near native light-harvesting properties. In contrast, replacement of both helices results in the loss of complexes from the membrane. The assembly of such doubly modified complexes is restored by a single serine residue at position -4 relative to the liganding histidine of the alpha-subunit. In-situ analysis of the spectral properties in a series of site directed mutants reveals a critical dependence of the model complex assembly on the residue′s side chain at this position. A hydrogen bond between the hydroxy group of the serine and the 131 keto group of one of the complexes′ central bacteriochlorophyll is identified by Raman spectroscopy. The additional OH-group of the serine residue, which participates in H-bonding, increases the model complexes′ thermal stability in the native membrane. Intramembrane H-bonding is thus shown to be a key factor for the binding of bacteriochlorophyll and assembly of this model cofactor-polypeptide site.

KEY WORDS: H-bonding, membrane proteine, bacteriochlorophyll-binding motif