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* State Key Laboratory of Biocontrol, Guangdong Province Key Laboratory for Pharmaceutical Functional Genes, College of Life Sciences, Sun Yat-sen (Zhongshan) University, Guangzhou, People’s Republic of China; and
Institute of Reproductive Immunology, Jinan University, Guangzhou, People’s Republic of China
C1q is the target recognition protein of the classical complement pathway and a major connecting link between innate and adaptive immunities. Its globular signature domain is also found in a variety of noncomplement protein that can be grouped together as a C1q family. In this study, we have cloned and identified a novel C1q family member in cephalochordate amphioxus and named it as AmphiC1q1. The high transcriptional levels of this gene were detected during all stages of embryonic development, and the section in situ hybridization demonstrated that AmphiC1q1 was mainly expressed in the ovary, intestine, and nerve system of mature individuals. The transcript of AmphiC1q1 was up-regulated by LPS and Gram-negative bacteria, but hardly by lipoteichoic acid and Staphylococcus aureus. The recombinant AmphiC1q1 protein could not bind with N-acetyl-glucosamine and did not possess hemagglutinating activity, indicating that AmphiC1q1 could not act as its lamprey homologue. But both the full-length protein and its truncated globular domain of C1q protein could interact with LPS. Moreover, recombinant AmphiC1q1 protein could inhibit collagen-induced platelet aggregation, but the truncated globular C1q domain protein would not, indicating that the blocking activity of AmphiC1q1 protein was via the collagen region of the protein. Our study on the primitive form of C1q family in protochordate will shed a light on understanding the gradual functional evolution of C1q family and eventual formation of mammalian homologues.
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1 This work was supported by Project 2007CB815800 of the National Basic Research Program (973) and Project 2006AA09Z433 of the State High-Tech Development Project (863) from the Ministry of Science and Technology of China; Project 2007DFA30840 of International S&T Cooperation Program of China; Key Project (0107) from the Ministry of Education and Key Projects of Commission of Science and Technology of Guangdong Province and Guangzhou City; and Project 20070420145 from China postdoctoral science foundation. A.X. is a recipient of the Outstanding Young Scientist Award from the National Natural Science Foundation of China.
2 Y.Y., H.H., and Y.W. contributed equally to this work.
3 Address correspondence and reprint requests to Dr. Anlong Xu, Department of Biochemistry, College of Life Sciences, Sun Yat-Sen (Zhongshan) University, 135 Xingangxi Road, 510275, Guangzhou, People’s Republic of China. E-mail address: lssxal{at}mail.sysu.edu.cn
4 Abbreviations used in this paper: gC1q, globular domain of C1q; CLR, collagen-like region; CRF, C1q-related factor; CTRP or cqt, C1q and TNF-related protein; GlcNAc, N-acetyl-glucosamine; ME, minimum-evolution; PRP, platelet-rich plasma; TRX, thioredoxin.
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