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J. Biol. Chem., Vol. 282, Issue 17, 12963-12975, April 27, 2007

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Isolation, Cloning, and Characterization of a Novel Phosphomannan-binding Lectin from Porcine Serum^*

Bruce Yong Ma¹, Natsuko Nakamura, Vladimir Dlabac^¶, Haruna Naito, Shinsuke Yamaguchi, Makiko Ishikawa, Motohiro Nonaka, Masaji Ishiguro^||, Nobuko Kawasaki, Shogo Oka^**, and Toshisuke Kawasaki²

From the Research Center for Glycobiotechnology, Ritsumeikan University, Shiga 525-8577, Japan, the Department of Biological Chemistry, Graduate School of Pharmaceutical Sciences, and the ^**School of Health Sciences, Faculty of Medicine, Kyoto University, Kyoto 606-8501, Japan, the ^¶Institute of Microbiology, Academy of Sciences of the Czech Republic, 142 20 Prague, Czech Republic, and the ^||Suntory Institute for Bioorganic Research, Shimamoto, Osaka 618-8503, Japan

Mannan-binding protein (MBP) is a C-type serum lectin that is an important constituent of the innate immune defense because it activates the complement system via the lectin pathway. While the pig has been proposed to be an attractive source of xenotransplantable tissues and organs, little is known about porcine MBP. In our previous studies, phosphomannan, but not mannan, was found to be an effective inhibitor of the C1q-independent bactericidal activity of newborn piglet serum against some rough strains of Gram-negative bacteria. In contrast, the inhibitory activities of phosphomannan and mannan were very similar in the case of MBP-dependent bactericidal activity against rough strains of Escherichia coli K-12 and S-16. Based on these findings, we inferred that an MBP-like lectin with slightly or completely different carbohydrate binding specificity might exist in newborn piglet serum and be responsible for the C1q-independent bactericidal activity. Herein we report that a novel phosphomannan-binding lectin (PMBL) of 33 kDa under reducing conditions was isolated from both newborn and adult porcine serum and characterized. Porcine PMBL functionally activated the complement system via the lectin pathway triggered by binding with both phosphomannan (P-mannan) and mannan, which, unlike MBP, was effectively inhibited by mannose 6-phosphate- or galatose-containing oligosaccharides. Our observations suggest that porcine PMBL plays a critical role in the innate immune defense from the newborn stage to adult-hood, and the establishment of a newborn piglet experimental model for the innate immune system studies is a valuable step toward elucidation of the physiological function and molecular mechanism of lectin pathway.

Received for publication, December 26, 2006 , and in revised form, February 17, 2007.

^* This work was supported in part by Grant-in-aid for Scientific Research on Priority Areas A-14082203 (to T. K.) and Grant-in-aid for Scientific Research C-18590471 (to B. Y. M.) from the Japan Society for the Promotion of Science, Ministry of Education, Culture, Sports, Science and Technology of Japan. 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.

¹ To whom correspondence may be addressed: Research Center for Glycobiotechnology, Ritsumeikan University, Nojishigashi 1-1-1, Kusatsu, Shiga 525-8577, Japan. Tel.: 81-77-561-3450; Fax: 81-77-561-3451; E-mail: byma{at}fc.ritsumei.ac.jp.

² To whom correspondence may be addressed: Research Center for Glycobiotechnology, Ritsumeikan University, Nojishigashi 1-1-1, Kusatsu, Shiga 525-8577, Japan. Tel.: 81-77-561-3444; Fax: 81-77-561-3496; E-mail: tkawasak{at}fc.ritsumei.ac.jp.

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