The Structure Determination of M. denitrificans Cytochrome C₅₅₀

Citation

Timkovich, Russell (1975) The Structure Determination of M. denitrificans Cytochrome C₅₅₀. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/xmcg-d794. https://resolver.caltech.edu/CaltechTHESIS:10202022-180817376

Abstract

The protein sequence and the three-dimensional folding structure for cytochrome c₅₅₀ from Micrococcus denitrificans are reported. The tertiary structure resulted from an x-ray crystallographic determination. Standard protein chemistry techniques were applied to sequence all the fragment peptides from a tryptic digest of c₅₅₀. This information was combined with a 2.45 Å electron density map of the protein where identifying the tryptic fragments in the map led to the correct ordering of the peptides and the final complete sequence.

The crystallization of c₅₅₀ is described. Three chemical derivatives of the protein were found, PtCl₄^2-; UO₂²⁺, and Pt(CN)₄^2-, and these aided in the isomorphous replacement solution to the crystallographic phase problem. The interpretation and refinement of the derivatives to produce an accurate protein map is discussed.

This bacterial c₅₅₀ possesses a structure similar to the known cytochromes from eukaryotic sources and from a photosynthetic bacterium. The three are contrasted to conclude that for the cytochrome family, there exists a core structure of polypeptide folding. Current proposed mechanisms for the action of c-type cytochromes are rejected as being incompatible with the c₅₅₀ structure. The view is advocated that the exposed heme edge in cytochrome may be the sole active site for the molecule.

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