Diversity of membrane transport proteins for vitamins in bacteria and archaea

Background: All organisms use cofactors to extend the catalytic capacities of proteins. Many bacteria and archaea can synthesize cofactors from primary metabolites, but there are also prokaryotes that do not have the complete biosynthetic pathways for all essential cofactors. These organisms are dependent on the uptake of cofactors, or at least their precursors that cannot be synthesized, from the environment. Even in those organisms that contain complete biosynthetic pathways membrane transporters are usually present, because the synthesis of cofactors is more costly than uptake. Scope of review: Here we give an overview of bacterial and archaeal transport systems for B-type vitamins, which are either cofactors or precursors thereof. Major conclusions: Prokaryotic vitamin transporters are extremely diverse, and found in many families of transporters. A few of these transport systems have been characterized in detail, but for most of them mechanistic insight is lacking. General significance: The lack of structural and functional understanding of bacterial vitamin transporters is unfortunate because they may be targets for new antibiotics. This article is part of a Special Issue entitled Structural biochemistry and biophysics of membrane proteins. Guest Editor: Bjorn Pedersen. (C) 2014 Elsevier B.V. All rights reserved.