crystal structure analysis of the polysialic acid specific o-acetyltransferase neuo晶体结构分析polysialic酸特定o-acetyltransferase neuo.pdf

Crystal Structure Analysis of the Polysialic Acid Specific O-Acetyltransferase NeuO 1 2¤ 1 ¨ 2 Eike C. Schulz , Anne K. Bergfeld , Ralf Ficner *, Martina Muhlenhoff * ¨ ¨ ¨ ¨ ¨ ¨ ¨ 1 Abteilung fur Molekulare Strukturbiologie, Institut fur Mikrobiologie und Genetik, Georg-August-Universitat Gottingen, Gottingen, Germany, 2 Institut fur Zellulare Chemie, Medizinische Hochschule Hannover, Hannover, Germany Abstract The major virulence factor of the neuroinvasive pathogen Escherichia coli K1 is the K1 capsule composed of a2,8-linked polysialic acid (polySia). K1 strains harboring the CUS-3 prophage modify their capsular polysaccharide by phase-variable O- acetlyation, a step that is associated with increased virulence. Here we present the crystal structure of the prophage- encoded polysialate O-acetyltransferase NeuO. The homotrimeric enzyme belongs to the left-handed b-helix (LbH) family of acyltransferases and is characterized by an unusual funnel-shaped outline. Comparison with other members of the LbH family allowed the identification of active site residues and proposal of a catalytic mechanism and highlighted structural characteristics of polySia specific O-acetyltransferases. As a unique feature of NeuO, the enzymatic activity linearly increases with the length of the N-terminal poly-y-domain which is composed of a variable number of tandem copies of an RLKTQDS heptad. Since the poly-y-domain was not resolved in the crystal structure it is assumed to be unfolded in the apo-enyzme.