A structural investigation of complex I and I+III2 supercomplex from Zea mays at 11-13 A resolution: assignment of the carbonic anhydrase domain and evidence for structural heterogeneity within complex I.
The projection structures of complex I and the I+III2 supercomplex from the C4 plant Zea mays were determined by electron microscopy and single particle image analysis to a resolution of up to 11 A. Maize complex I has a typical L-shape. Additionally, it has a large hydrophilic extra-domain attached to the centre of the membrane arm on its matrix-exposed side, which previously was described for Arabidopsis and which was reported to include carbonic anhydrase subunits. A comparison with the X-ray structure of homotrimeric gamma-carbonic anhydrase from the archaebacterium Methanosarcina thermophila indicates that this domain is also composed of a trimer. Mass spectrometry analyses allowed to identify two different carbonic anhydrase isoforms, suggesting that the gamma-carbonic anhydrase domain of maize complex I most likely is a heterotrimer. Statistical analysis indicates that the maize complex I structure is heterogeneous: a less-abundant "type II" particle has a 15 A shorter membrane arm and an additional small protrusion on the intermembrane-side of the membrane arm if compared to the more abundant "type I" particle. The I+III2 supercomplex was found to be a rigid structure which did not break down into subcomplexes at the interface between the hydrophilic and the hydrophobic arms of complex I. The complex I moiety of the supercomplex appears to be only of "type I". This would mean that the "type II" particles are not involved in the supercomplex formation and, hence, could have a different physiological role.
Institute for Plant Genetics, Faculty of Natural Sciences, Leibniz Universität Hannover, Herrenhäuser Str. 2, D-30419 Hannover, Germany.
Katrin
K
Peters
Natalya V
NV
Dudkina
Lothar
L
Jänsch
Hans-Peter
HP
Braun
Egbert J
EJ
Boekema
D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000378:metabolism; D002256:Carbonic Anhydrases / Q000737:chemistry*; D042967:Electron Transport Complex I / Q000737:chemistry*; D014450:Electron Transport Complex III / Q000737:chemistry*; D008854:Microscopy, Electron; D008969:Molecular Sequence Data; D017434:Protein Structure, Tertiary; D003313:Zea mays / Q000737:chemistry / Q000378:metabolism*
D002256:Carbonic Anhydrases; D042967:Electron Transport Complex I; D014450:Electron Transport Complex III