Cooperative protein structural dynamics of homodimeric hemoglobin linked to water cluster at subunit interface revealed by time-resolved X-ray solution scattering

Journal Article · Thu Apr 14 00:00:00 EDT 2016 · Structural Dynamics

DOI:https://doi.org/10.1063/1.4947071· OSTI ID:1248391

Kim, Jong Goo ^[1]; Muniyappan, Srinivasan ^[1]; Oang, Key Young ^[1]; Kim, Tae Wu ^[1]; Yang, Cheolhee ^[1]; Kim, Kyung Hwan ^[1]; Kim, Jeongho ^[2]; Ihee, Hyotcherl ^[1]

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1. KAIST, Daejeon (South Korea); Inst. for Basic Science (IBS), Daejeon (South Korea)
2. Inha Univ., Incheon (South Korea)

Homodimeric hemoglobin (HbI) consisting of two subunits is a good model system for investigating the allosteric structural transition as it exhibits cooperativity in ligand binding. In this work, as an effort to extend our previous study on wild-type and F97Y mutant HbI, we investigate structural dynamics of a mutant HbI in solution to examine the role of well-organized interfacial water cluster, which has been known to mediate intersubunit communication in HbI. In the T72V mutant of HbI, the interfacial water cluster in the T state is perturbed due to the lack of Thr72, resulting in two less interfacial water molecules than in wild-type HbI. By performing picosecond time-resolved X-ray solution scattering experiment and kinetic analysis on the T72V mutant, we identify three structurally distinct intermediates (I₁, I₂, and I₃) and show that the kinetics of the T72V mutant are well described by the same kinetic model used for wild-type and F97Y HbI, which involves biphasic kinetics, geminate recombination, and bimolecular CO recombination. The optimized kinetic model shows that the R-T transition and bimolecular CO recombination are faster in the T72V mutant than in the wild type. From structural analysis using species-associated difference scattering curves for the intermediates, we find that the T-like deoxy I₃ intermediate in solution has a different structure from deoxy HbI in crystal. In addition, we extract detailed structural parameters of the intermediates such as E-F distance, intersubunit rotation angle, and heme-heme distance. By comparing the structures of protein intermediates in wild-type HbI and the T72V mutant, we reveal how the perturbation in the interfacial water cluster affects the kinetics and structures of reaction intermediates of HbI.

• Research Organization: Argonne National Laboratory (ANL), Argonne, IL (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES); National Research Foundation of Korea (NRF); NIH National Inst. of General Medical Sciences
• Grant/Contract Number: AC02-06CH11357; NRF-2014R1A1A1002511; R24GM111072
• OSTI ID: 1248391
• Journal Information: Structural Dynamics, Vol. 3, Issue 2; ISSN 2329-7778
• Publisher: American Crystallographic Association/AIP
• Country of Publication: United States
• Language: ENGLISH

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59 BASIC BIOLOGICAL SCIENCES