Related Experiment Videos
Insights
Cytochrome c551 shares structural similarities with both globin and cytochrome b5 folds, suggesting a common ancestor or convergent evolution driven by heme binding. This protein fold analysis offers insights into evolutionary relationships among heme proteins.
Area of Science:
- Biochemistry
- Structural Biology
- Evolutionary Biology
Background:
- Cytochrome c551, globin, and cytochrome b5 are heme proteins with distinct structures.
- Understanding their evolutionary relationships is crucial for deciphering protein evolution.
Purpose of the Study:
- To investigate the structural and topological similarities between cytochrome c551, globin, and cytochrome b5.
- To explore potential evolutionary connections and the factors driving their structural convergence or divergence.
Main Methods:
- Three-dimensional structural characterization of cytochrome c551.
- Superposition of cytochrome c551, globin, and cytochrome b5 structures.
- Analysis of root mean square (RMSD) separation between C-alpha atoms.
- Comparison of heme iron positions, heme normals, and heme orientation.
- Assessment of sequence divergence using minimum base change per codon.
Main Results:
- Cytochrome c551 exhibits structural equivalence to both globin (49 residues) and cytochrome b5 (41 residues) folds.
- A common heme-binding core is identified, potentially linked to globin gene structure.
- Heme iron positions and orientations show variations but similar heme face directionality.
- Sequence divergence analysis suggests similarities may arise from functional or structural constraints rather than recent common ancestry.
Conclusions:
- The structural similarities between these heme proteins may result from convergent evolution driven by the functional necessity of heme binding.
- Alternatively, a distant common ancestor could explain the observed fold similarities.
- Further analysis of sequence and structural data is needed to definitively distinguish between convergence and divergence.
Abstract:
Of the 82 three dimensionally characterized residues of cytochrome c551, 49 are found to be structurally and topologically equivalent to the globin fold and 41 are equivalent to the cytochrome b5 fold, with a respective root mean square separation of 3.5 and 4.9 A between equivalenced Calpha atoms. The common fold represents a central heme binding core, corresponding to the middle exon of certain globin genes. After superposition of the protein folds, the heme irons are found to be separated by 5.4 and 1.6 A, while their heme normals are inclined by 6 degrees and 32 degrees, respectively. Furthermore, the heme "face", determined by the asymmetric attachment of the vinyl and propionyl side chains, is directed similarly in all three heme proteins. The heme itself is rotated by 72 degrees and 116 degrees about its normal, respectively. The minimum base change per codon for the three pairwise comparisons corresponds to the expected value of random sequence comparisons. While all three heme proteins may have diverged from a common ancestor, their similarity may have arisen from the requirements of heme binding or the utilization of a particularly stable fold. Known structures within commonly accepted divergent families were superimposed in order to discriminate better between convergence and divergence. Minimum base changes per codon, number of deletions and insertions, percentage of equivalenced residues, precision of heme superposition, and root mean square separation of equivalenced Calpha atoms were tested as measures of evolutionary relationships.