The Structure Determination of M. denitrificans Cytochrome C₅₅₀

Author: Timkovich, Russell

Year: 1975

Degree: Dissertation (Ph.D.)

Advisor: Dickerson, Richard E.

Committee Member: Unknown, Unknown

Option: Chemistry

DOI: 10.7907/xmcg-d794

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, PtCl42-; UO22+, and Pt(CN)42-, 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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