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J. Biol. Chem., Vol. 279, Issue 17, 17738-17749, April 23, 2004

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CMP-N-Acetylneuraminic Acid Synthetase from Escherichia coli K1 Is a Bifunctional Enzyme

IDENTIFICATION OF MINIMAL CATALYTIC DOMAIN FOR SYNTHETASE ACTIVITY AND NOVEL FUNCTIONAL DOMAIN FOR PLATELET-ACTIVATING FACTOR ACETYLHYDROLASE ACTIVITY^*

Guangchao Liu, Chunsheng Jin, and Cheng Jin

From the State Key Laboratory of Microbial Resources, Institute of Microbiology, Chinese Academy of Sciences, Beijing 100080, People's Republic of China

Escherichia coli CMP-NeuAc synthetase (EC 2.7.7.43) catalyzes the synthesis of CMP-NeuAc from CTP and NeuAc, which is essential for the formation of capsule polysialylate for strain K1. Alignment of the amino acid sequence of E. coli CMP-NeuAc synthetase with those from other bacterial species revealed that the conserved motifs were located in its N termini, whereas the C terminus appeared to be redundant. Based on this information, a series of deletions from the 3'-end of the CMPNeuAc synthetase coding region was constructed and expressed in E. coli. As a result, the catalytic domain required for CMP-NeuAc synthetase was found to be in the N-terminal half consisting of amino acids 1-229. Using the strategy of tertiary structure prediction based on the homologous search of the secondary structure, the C-terminal half was recognized as an 1-subunit of bovine brain platelet-activating factor acetylhydrolase isoform I. The biochemical analyses showed that the C-terminal half consisting of amino acids 228-418 exhibited platelet-activating factor acetylhydrolase activity. The enzyme properties and substrate specificity were similar to that of bovine brain 1-subunit. Although its physiological function is still unclear, it has been proposed that the 1-subunit-like domain of E. coli may be involved in the traversal of the blood-brain barrier.

Received for publication, January 7, 2004 , and in revised form, January 30, 2004.

^* This work was supported by the Chinese Academy of Sciences Grant KSCX2-3-02-01 and the National Science and Technology Ministry, China, Grant 2001CCA00100. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

Both authors contributed equally to this work.

To whom correspondence should be addressed. Tel.: 86-10-62587206; Fax: 86-10-62653468; E-mail: jinc{at}sun.im.ac.cn.

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