The authors thank Todd Hoopes and Anil Shakya for ideas and support in design and expression protocols.Some results reported herein(structure 7KAE)are derived from work performed at Argonne National Laboratory,Structural Biology Center(SBC)at the Advanced Photon Source.SBC is operated by UChicago Argonne,LLC,for the U.S.Department of Energy,Office of Biological and Environmental Research under contract DE-AC02-06CH11357.Additional results reported herein(structure 9CFS)are derived from work performed at the Center for BioMolecular Structure(CBMS)at Brookhaven National Laboratory.CBMS is primarily supported by the National Institutes of Health,Na-tional Institute of General Medical Sciences(NIGMS)through Grant#P30GM133893,and by the DOE Office of Biological and Environ-mental Research FWP#BO070.This research used resource 17-ID-2 of the National Synchrotron Light Source II,a U.S.Department of Energy(DOE)Office of Science User Facility operated for the DOE Office of Science under Contract No.DE-SC0012704.This work was supported by the Material Measurement Laboratory of the National Institute of Stan-dards and Technology of the USA.Certain commercial materials and equipment are identified in order to adequately specify experimental procedures （structure 7KAE）

such identifications neither imply recommendation nor endorsement by the National Institute of Standards and Technology nor do they imply that the material or equipment identified is the best available for the purpose.Both authors participated in protein design and production and in writing this paper.All authors read and approved the final manuscript. （）