Crystal Structures of Modified Myoglobins. II. Relation between Oxygen Affinity Properties and Structural Changes around Heme in Myoglobins Reconstituted with 2,4-Diisopropyldeuteroheme, 2-Isopropyl-4-VinyIdeuteroheme, and 2-Vinyl-4-Isopropyldeuteroheme

• Main Authors: MIKI, Kunio, HARADA, Shigeharu, HATO, Yukinori, IBA, Seigo, KAI, Yasushi, KASAI, Nobutami, KATSUBE, Yukiteru, KAWABE, Kuniyasu, YOSHIDA, Zen-ichi, OGOSHI, Hisanobu
• Format: Text
• Language: English
• Published: Oxford University Press 1986
• Subjects: REGULAR PAPERS; Sperm whale
• Online Access: http://jb.oxfordjournals.org/cgi/content/short/100/2/277

The crystal structures of sperm whale metmyoglobins reconstituted with three kinds of modified hemes, 2,4-diisopropyldeuteroheme, 2-isopropyl-4-vinyldeuteroheme, and 2-vinyl-4-isopropyldeuteroheme, have been determined and refined at 2.2 Å resolution to R = 0.216, 0.219, and 0.195, respectively. All the crystals of these myoglobins are isomorphous with that of native metmyoglobin. The 2-vinyl-4-isopropyldeuteroheme was found to be in a reverse orientation, in which the heme plane is rotated by 180° about an axis through the α-γ-meso carbons, whereas the orientations of the other two hemes were the same as that of protoheme in native myoglobin. In the myoglobins with 2,4-diisopropyldeuteroheme and 2-vinyl-4-isopropyldeuteroheme, both of which have lower oxygen affinities than native myoglobin, the bulky isopropyl side chain pushes Phe 43 0.7 Å toward His 64 (the distal histidine) in the former, and the whole E helix at most 1.5 Å, including a 0.7 Å shift of the His 64 imidazole ring, in the latter. The changes of the structures prevent His 64 from forming a hydrogen bond with the liganded oxygen molecule, so that these two modified myoglobins show low oxygen affinities. On the other hand, there is no such drastic displacement in myoglobin with 2-isopropyl-4-vinyldeutero-heme, which has a slightly higher oxygen affinity than native myoglobin.