Abortive assembly of succinate-ubiquinone reductase (Complex II) in a ferrochelatase-deficient mutant of Escherichia col
- PDF / 328,763 Bytes
- 11 Pages / 595 x 785 pts Page_size
- 27 Downloads / 145 Views
O R I GI N A L P A P E R
C. Nihei á T. Nakayashiki á K. Nakamura á H. Inokuchi R. B. Gennis á S. Kojima á K. Kita
Abortive assembly of succinate-ubiquinone reductase (Complex II) in a ferrochelatase-de®cient mutant of Escherichia coli Received: 27 May 2000 / Accepted: 7 December 2000 / Published online: 1 March 2001 Ó Springer-Verlag 2001
Abstract Heme molecules play important roles in electron transfer by redox proteins such as cytochromes. In addition, a structural role for heme in protein folding and the assembly of enzymes has been suggested. Previous results obtained using Escherichia coli hemA mutants, which are unable to synthesize 5-aminolevulinic acid, a precursor of porphyrins and hemes, have demonstrated a requirement for heme biosynthesis in the assembly of a functional succinate-ubiquinone reductase (SQR or complex II), which is a component of the aerobic respiratory chain. In the present study, in order to investigate the role of the heme in the assembly of E. coli SQR, we used a hemH (encodes ferrochelatase) mutant that lacks the ability to insert iron into the porphyrin ring. The hemH mutant failed to insert functional SQR into the cytoplasmic membrane, and
the catalytic portion of SQR [the ¯avoprotein subunit (Fp) and the iron-sulfur protein subunit (Ip)] was localized in the cytoplasm of the cell. It is of interest to note that protoporphyrin IX accumulated in the mutant cells and inactivated the cytoplasmic succinate dehydrogenase (SDH) activity associated with the catalytic Fp-Ip complex. In contrast, SQR was assembled into the membrane of a heme-permeable hemH double mutant when hemin was present in the culture. Only a low level of SQR activity was found in the membrane when hemin was replaced by non-iron metalloporphyrins: Mn-, Co-, Ni-, Zn- and Cu-protoporphyrin IX, or protoporphyrin IX These results indicate that heme iron is indispensable for the functional assembly of SQR in the cytoplasmic membrane of E. coli, and provide a new insight into the biological role of heme in the molecular assembly of the multi-subunit enzyme complex.
Communicated by H. Ikeda
Key words Enzyme assembly á Succinate dehydrogenase á Cytochrome b á hemH mutant á Ferrochelatase
C. Nihei á K. Kita (&) Department of Biomedical Chemistry, Graduate School of Medicine, The University of Tokyo, 7-3-1, Hongo, Bunkyo-ku, Tokyo, 113-0033, Japan E-mail: [email protected] Tel.: +81-3-5841-3526 Fax: +81-3-5841-3444 T. Nakayashiki1 á H. Inokuchi Department of Biological Science, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto, 606-8224, Japan K. Nakamura2 á S. Kojima Department of Parasitology, Institute of Medical Science, University of Tokyo, 4-6-1, Shirokanedai, Minato-ku, Tokyo, 108-0071, Japan R. B. Gennis Department of Biochemistry, University of Illinois, 600 South Mathews Street Urbana, IL 61801, USA Present addresses: Department of Tumor Biology, Institute of Medical Science, University of Tokyo, 4-6-1, Shirokanedai, Minato-ku, Tokyo, 108-0071, Japan
1
2
Kyoritsu College of Pharmacy, 1-5-30, S
Data Loading...
