Flexibility in Mannan-Binding Lectin-Associated Serine Proteases-1 and -2 Provides Insight on Lectin Pathway Activation

Ruodan Nan,Christopher M Furze,David W Wright,Jayesh Gor,Russell Wallis,Stephen J Perkins

doi:10.1016/j.str.2016.12.014

Ruodan Nan, Christopher M Furze + Show 4 more

Open Access

https://doi.org/10.1016/j.str.2016.12.014

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Abstract

SummaryThe lectin pathway of complement is activated by complexes comprising a recognition component (mannose-binding lectin, serum ficolins, collectin-LK or collectin-K1) and a serine protease (MASP-1 or MASP-2). MASP-1 activates MASP-2, and MASP-2 cleaves C4 and C4b-bound C2. To clarify activation, new crystal structures of Ca2+-bound MASP dimers were determined, together with their solution structures from X-ray scattering, analytical ultracentrifugation, and atomistic modeling. Solution structures of the CUB1-EGF-CUB2 dimer of each MASP indicate that the two CUB2 domains were tilted by as much as 90° compared with the crystal structures, indicating considerable flexibility at the EGF-CUB2 junction. Solution structures of the full-length MASP dimers in their zymogen and activated forms revealed similar structures that were much more bent than anticipated from crystal structures. We conclude that MASP-1 and MASP-2 are flexible at multiple sites and that this flexibility may permit both intra- and inter-complex activation.

Highlights

Complement destroys invading microorganisms and initiates defense mechanisms including chemotaxis, phagocytosis, cell adhesion, B cell differentiation, and maintenance of immune tolerance (Carroll, 2004; Porter and Reid, 1978)
By comparing the MASP solution structures with models for mannan-binding lectin (MBL), we evaluated the MASP-MBL complexes that trigger complement activation
In the former, one-half of dimeric rat MASP-2 binds to at least two sites in a nearplanar rat MBL structure, and MBL collagen flexibility is reduced when the carbohydrate recognition domains (CRDs) domains bind to a mannosecoated surface

Summary

SUMMARY

The lectin pathway of complement is activated by complexes comprising a recognition component (mannose-binding lectin, serum ficolins, collectinLK or collectin-K1) and a serine protease (MASP-1 or MASP-2). MASP-1 activates MASP-2, and MASP-2 cleaves C4 and C4b-bound C2. New crystal structures of Ca2+-bound MASP dimers were determined, together with their solution structures from X-ray scattering, analytical ultracentrifugation, and atomistic modeling. Solution structures of the CUB1-EGF-CUB2 dimer of each MASP indicate that the two CUB2 domains were tilted by as much as 90 compared with the crystal structures, indicating considerable flexibility at the EGF-CUB2 junction. Solution structures of the fulllength MASP dimers in their zymogen and activated forms revealed similar structures that were much more bent than anticipated from crystal structures. We conclude that MASP-1 and MASP-2 are flexible at multiple sites and that this flexibility may permit both intra- and inter-complex activation

INTRODUCTION

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EXPERIMENTAL PROCEDURES