MBE Advance Access published online on October 1, 2003
Molecular Biology and Evolution, doi:10.1093/molbev/msg244
Molecular Biology and Evolution © Society for Molecular Biology and Evolution 2003; all rights reserved
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
1 Universidad Nacional de Quilmes, Bernal, Argentina
* To whom correspondence should be addressed. E-mail: silvina{at}unq.edu.ar.
Riboflavin, an essential cofactor for all organisms, is biosynthesized in plants, fungi and microorganisms. The penultimate step in the pathway is catalyzed by the enzyme lumazine synthase. One of the most distinctive characteristics of this enzyme is that it is found in different species in two different quaternary structures, pentameric and icosahedral, built from practically the same structural monomeric unit. In fact, the icosahedral structure is best described as a capsid of twelve pentamers. Despite this noticeable difference, the active sites are virtually identical in all structurally studied members. Furthermore, the main regions involved in the catalysis are located at the interface between adjacent subunits in the pentamer. Thus, both quaternary forms of the enzyme must meet similar structural requirements to achieve their function while, at the same time, they should differ in the sequence traits responsible of the different quaternary structures observed. Here, we present a combined analysis that includes sequence-structure and evolutionary studies to find the sequence determinants of the different quaternary assemblies of this enzyme. A data set containing 86 sequences of the lumazine synthase family was recovered by sequence similarity searches. Seven of them had resolved three-dimensional structures. A subsequent phylogenetic reconstruction by maximum parsimony (MP) allowed the division of the total set into two clusters in accord with their quaternary structure. The comparison between of the patterns of three-dimensional contacts derived from the known 3D structures and variation in sequence conservation revealed a significant shift in structural constraints of certain positions. Also, in order to explore the changes in functional constraints between the two groups, site-specific evolutionary rate shifts were analyzed. We found that the positions involved in icosahedral contacts suffer a larger increase in constraints than the rest. We found 8 sequence sites that would be the most important icosahedral sequence determinants. We discuss our results and compare with previous work. The findings presented should contribute to refine the current structural data, to design assays to explore the role of these positions, to the structural characterization of new sequences, and to begin the study of the underlying evolutionary mechanisms. Key Words:
lumazine synthase, quaternary structure, structural constraints, evolutionary rates
© 2003 Society for Molecular Biology and Evolution
Original Articles
Sequence Determinants of Quaternary Structure in Lumazine Synthase
2 Fundación Instituto Leloir (IIBBA-CONICET, IIB-FCEN-UBA), Av. Patricias Argentinas 435, Buenos Aires 1405, Argentina
3 Laboratorio de Fisiología y Biología Molecular, Facultad de Ciencias Exactas y Naturales, Ciudad Universitaria, Pabellón II, (C1428EHA) Buenos Aires, Argentina
Abstract 
CiteULike 
Connotea 
Del.icio.us What's this?
This article has been cited by other articles:
|
|
 |
|
  J.-B. Peltier, Y. Cai, Q. Sun, V. Zabrouskov, L. Giacomelli, A. Rudella, A. J. Ytterberg, H. Rutschow, and K. J. van Wijk The Oligomeric Stromal Proteome of Arabidopsis thaliana Chloroplasts Mol. Cell. Proteomics, January 1, 2006; 5(1): 114 - 133. [Abstract] [Full Text] [PDF]
|
|