Tài liệu Báo cáo khoa học: Solution properties of full-length integrin aIIbb3 refined models suggest

Solution properties of full-length integrin aIIbb3 refined

models suggest environment-dependent induction of

alternative bent ⁄extended resting states

Camillo Rosano1 and Mattia Rocco2

1 Nanobiotecnologie, Istituto Nazionale per la Ricerca sul Cancro (IST), Genova, Italy

2 Biopolimeri e Proteomica, IST, Genova, Italy

Introduction

Integrins are heterodimeric transmembrane (TM) cellu￾lar receptors involved in mechanical anchoring and

two-way signaling [1]. Each a and b subunit has a

modular structure with a large extracellular portion,

a single TM region and a cytoplasmic domain [1–3].

The integrin activation mechanism is regulated by

conformational changes, the details of which have not

yet been fully elucidated [2,3]. X-ray crystallography

Keywords

blood coagulation; hydrodynamics;

modeling; modular proteins; protein

structure

Correspondence

M. Rocco, Biopolimeri e Proteomica, IST

c ⁄ o CBA, Largo R. Benzi 10, I-16132

Genova, Italy

Fax: +39-0105737-325

Tel: +39-0105737-310

E-mail: [email protected]

(Received 12 November 2009, revised 1

May 2010, accepted 29 May 2010)

doi:10.1111/j.1742-4658.2010.07724.x

The recently published novel integrin aIIbb3 ectodomain crystallographic

structure and NMR structures of its transmembrane ⁄ cytoplasmic segments

were employed to refine previously developed molecular models. Alterna￾tive complete aIIbb3 models were built and evaluated, and their shape was

compared with EM maps and their computed hydrodynamic ⁄ conforma￾tional properties were compared with the available experimental data. A

partially extended ⁄ closed model, or a mixture of bent⁄ closed and exten￾ded ⁄ closed conformations, are both compatible with the results of a recent

small-angle neutron scattering study of Triton X-100-solubilized resting

aIIbb3, while new electron microscopy evidence of nanodiscs-embedded

aIIbb3 supports the bent⁄ closed resting form. However, only an extended ⁄-

closed model matches well the hydrodynamics of either octyl-glucoside-sol￾ubilized or nanodiscs-embedded resting aIIbb3, suggesting that different

solubilization strategies and substrate interactions might operate a confor￾mational selection between alternative, stable states. Furthermore, extende￾d ⁄ open models are required to match the electron tomography map and

the hydrodynamics following the priming-induced b3 hybrid domain swing￾out, but without immediate full tail separation. Importantly, both extension

and opening transitions can occur by pivoting at the recently identified b3

hinge point, which does not appear to be freely flexible. The structure and

mechanism of action of integrins thus seem to depend on discrete transi￾tions and to be more tightly coupled to the local environment than previ￾ously thought.

Abbreviations

bc, bent ⁄ closed; DMPC, 1,2-dimyristoyl-sn-glycero-3-phosphocholine; DMPG, 1,2-dimyristoyl-sn-glycero-3-phospho-(1¢-rac-glycerol); DPPC,

1,2-dipalmitoyl-sn-glycero-3-phosphocholine; ec, extended ⁄ closed; EGF, epidermal growth factor; EM, electron microscopy; eotc,

extended ⁄ open ⁄ tails crossed; eots, extended ⁄ open ⁄ tail separated; ET, electron tomography; NMA, Normal Modes Analysis; OG, octyl￾glucoside; pec, partially extended ⁄ closed; PSI, plexin ⁄ semaphorin ⁄ integrin; SANS, small-angle neutron scattering; TEM, transmission

electron microscopy; TM, transmembrane.

3190 FEBS Journal 277 (2010) 3190–3202 ª 2010 The Authors Journal compilation ª 2010 FEBS