Surface analysis of the photosystem I complex by electron and atomic force microscopy

• Published in: Journal of molecular biology Vol. 283; no. 1; pp. 83 - 94
• Main Authors: Fotiadis, Dimitrios, Müller, Daniel J, Tsiotis, Georgios, Hasler, Lorenz, Tittmann, Peter, Mini, Thierry, Jenö, Paul, Gross, Heinz, Engel, Andreas
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 1998
• Subjects: Amino Acid Sequence; atomic force microscopy; Crystallization; crystals; Cyanobacteria - chemistry; electron microscopy; Freshwater; Image Processing, Computer-Assisted; Microscopy, Atomic Force; Microscopy, Electron; molecular conformation; molecular dissection; Molecular Sequence Data; Photosynthetic Reaction Center Complex Proteins - chemistry; Photosynthetic Reaction Center Complex Proteins - ultrastructure; photosystem I; Photosystem I Protein Complex; proteins; surfaces; Synechococcus; two-dimensional crystals; P700; SSNR; OTG; PS; two-dimensional crystals; Chl; Hepes; Pha; AFM; F X, F A, F B; molecular dissection; LPR; 2D; electron microscopy; DMPC; Psa; EM; photosystem I; atomic force microscopy; SB-12; CAS; FRC; Mes; A 0, A 1; BA
• ISSN: 0022-2836; 1089-8638
• DOI: 10.1006/jmbi.1998.2097

Two-dimensional (2D) crystals of the photosystem I (PSI) reaction center from Synechococcus sp. OD24 were analyzed by electron and atomic force microscopy. Surface relief reconstructions from electron micrographs of freeze-dried unidirectionally shadowed samples and topographs recorded with the atomic force microscope (AFM) provided a precise definition of the lumenal and stromal PSI surfaces. The lumenal surface was composed of four protrusions that surrounded an indentation. One of the protrusions, the PsaF subunit, was often missing. Removal of the extrinsic proteins with the AFM stylus exposed the stromal side of the PSI core, whose surface structure could then be imaged at a resolution better than 1.4 nm. This interfacial surface between core and extrinsic subunits, had a pseudo-2-fold symmetry and protrusions that correlated with the surface helices e and e′ or were at the sites of putative α-helix-connecting loops estimated from the 4 Å map of the complex. The molecular dissection achieved with the AFM, opens new possibilities to unveil the interfaces between subunits of supramolecular assemblies.