Protein Science / NMR analysis of the interaction of picornaviral proteinases Lb and 2A with their substrate eukaryotic initiation factor 4GII

Messenger RNA is recruited to the eukaryotic ribosome by a complex including the eukaryotic initiation factor (eIF) 4E (the capbinding protein), the scaffold protein eIF4G and the RNA helicase eIF4A. To shutoff hostcell protein synthesis, eIF4G is cleaved during picornaviral infection by a virally encoded proteinase; the structural basis of this reaction and its stimulation by eIF4E is unclear. We have structurally and biochemically investigated the interaction of purified footandmouth disease virus (FMDV) leader proteinase (Lbpro), human rhinovirus 2 (HRV2) 2A proteinase (2Apro) and coxsackievirus B4 (CVB4) 2Apro with purified eIF4GII, eIF4E and the eIF4GII/eIF4E complex. Using nuclear magnetic resonance (NMR), we completed 13C/15N sequential backbone assignment of human eIF4GII residues 551745 and examined their binding to murine eIF4E. eIF4GII551745 is intrinsically unstructured and remains so when bound to eIF4E. NMR and biophysical techniques for determining stoichiometry and binding constants revealed that the papainlike Lbpro only forms a stable complex with eIF4GII551745 in the presence of eIF4E, with KD values in the low nanomolar range; Lbpro contacts both eIF4GII and eIF4E. Furthermore, the unrelated chymotrypsinlike 2Apro from HRV2 and CVB4 also build a stable complex with eIF4GII/eIF4E, but with KD values in the low micromolar range. The HRV2 enzyme also forms a stable complex with eIF4E; however, none of the proteinases tested complex stably with eIF4GII alone. Thus, these three picornaviral proteinases have independently evolved to establish distinct triangular heterotrimeric protein complexes that may actively target ribosomes involved in mRNA recruitment to ensure efficient host cell shutoff.(VLID)484329