Structure and Function of the Long Pentraxin PTX3 Glycosidic Moiety: Fine-Tuning of the Interaction with C1q and Complement Activation

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• 作者：Antonio Inforzato ; Giuseppe Peri ; Andrea Doni ; Cecilia Garlanda ; Alberto Mantovani ; Antonio Bastone ; Andrea Carpentieri ; Angela Amoresano ; Piero Pucci ; Anja Roos ; Mohamed R. Daha ; Silvia Vincenti ; Gra
• 刊名：Biochemistry
• 出版年：2006
• 出版时间：September 26, 2006
• 年：2006
• 卷：45
• 期：38
• 页码：11540 - 11551
• 全文大小：4646K
• 年卷期：v.45,no.38(September 26, 2006)
• ISSN：1520-4995

文摘

The prototypic long pentraxin PTX3 is a unique fluid-phase pattern recognition receptor thatplays a nonredundant role in innate immunity and female fertility. The PTX3 C-terminal domain is requiredfor C1q recognition and complement activation and contains a single N-glycosylation site on Asn 220. Inthe present study, we characterized the structure of the human PTX3 glycosidic moiety and investigatedits relevance in C1q interaction and activation of the complement classical pathway. By specific endoand exoglycosidases digestion and direct mass spectrometric analysis, we found that both recombinantand naturally occurring PTX3 were N-linked to fucosylated and sialylated complex-type sugars.Interestingly, glycans showed heterogeneity mainly in the relative amount of bi, tri, and tetrantennarystructures depending on the cell type and inflammatory stimulus. Enzymatic removal of sialic acid or theentire glycosidic moiety equally enhanced PTX3 binding to C1q compared to that in the native protein,thus indicating that glycosylation substantially contributes to modulate PTX3/C1q interaction and thatsialic acid is the main determinant of this contribution. BIAcore kinetic measurements returned decreasingK_off values as sugars were removed, pointing to a stabilization of the PTX3/C1q complex. No majorrearrangement of PTX3 quaternary structure was observed after desialylation or deglycosylation asestablished by size exclusion chromatography. Consistent with C1q binding, PTX3 desialylation enhancedthe activation of the classical complement pathway, as assessed by C4 and C3 deposition. In conclusion,our results provided evidence of an involvement of the PTX3 sugar moiety in C1q recognition andcomplement activation.