LptA is an essential periplasmic localized transport protein that has been implicated together with MsbA, LptB, and the Imp/RlpB complex in lipopolysaccharide (LPS) transport from the inner to the outer membrane, thereby contributing to building the cell envelope in Gram-negative bacteria and maintaining its integrity. Herein we present the first crystal structures of processed Escherichia coli LptA in two crystal forms with two and eight molecules in the asymmetric unit. In both crystal forms severe anisotropic diffraction was corrected which facilitated model building and structural refinement. The eight molecule form of LptA is induced when LPS or Ra LPS is included during crystallization. The unique LptA structure represents a novel fold, consisting of eleven consecutive antiparallel strands, folded along the middle to resemble a slightly twisted jellyroll. Each LptA molecule interacts with an adjacent LptA molecule in head-to-tail fashion to resemble long fibers. Site directed mutagenesis of conserved residues located within a cluster that delineate the N terminal -strands of LptA do not impair the function of the protein although their overexpression appears more detrimental to LPS transport than wild type LptA. Moreover, altered expression of both, wild type and mutated proteins interfered with normal LPS transport as witnessed by the production of an anomalous form of LPS. Structural analysis suggests that head-to-tail stacking of LptA molecules could be destabilized by the mutation, thereby potentially contributing to impair LPS transport.
|Titolo:||Novel structure of the conserved Gram-negative lipopolysaccharide transport protein A and mutagenesis analysis|
|Parole Chiave:||LptA/YhbN; lipopolysaccharide transport; periplasm; X-ray crystal structure; anisotropic diffraction|
|Settore Scientifico Disciplinare:||Settore BIO/18 - Genetica|
|Data di pubblicazione:||2008|
|Digital Object Identifier (DOI):||10.1016/j.jmb.2008.04.045|
|Appare nelle tipologie:||01 - Articolo su periodico|