Effect of heme binding on the structure and stability of Escherichia coli apocytochrome b562.


The structure and stability of apocytochrome b562 were explored using absorption and circular dichroism spectroscopic methods. The polypeptide chain retains a well-defined structure when the prosthetic heme group is removed from cytochrome b562. Circular dichroism measurements estimate 60% helicity for apocytochrome b562, compared with 80% helicity found in holocytochrome b562. At low pH, apocytochrome b562 displays a midpoint pH of 2.9, while ferricytochrome b562 displays a midpoint pH of 2.3. The unfolding of the apoprotein by urea and heat can be well approximated by the two-state transition model. The stability of apocytochrome b562 is significantly reduced from that of the holoprotein. The free energy of stabilization (delta G degrees) and the midpoint transition temperature (Tm) for apocytochrome b562 are found to be 3.2 +/- 0.5 kcal/mol and 52.3 +/- 0.9 degrees C, respectively, compared with 6.6 +/- 0.5 kcal/mol and 67.2 +/- 0.5 degrees C for ferricytochrome b562. The smaller heat capacity change upon unfolding of apocytochrome b562 than that of ferricytochrome b562, estimated from the thermodynamic parameters, indicates that apocytochrome b562 possesses a smaller hydrophobic core than holocytochrome b562. Size-exclusion chromatography studies indicate that the apoprotein is slightly more extended in molecular dimension than ferricytochrome b562. The data suggest that apocytochrome b562 resembles a "molten globule" or a "collapsed form" of the holoprotein, in which secondary structure formation is largely complete while the global folding is either only partially complete or dynamically expanded. Study holds ProTherm entries: 3958, 3959, 3960, 3961 Extra Details: hydrophobic core; molten globule;collapsed form;,partially complete

Submission Details

ID: qjQXMLhk

Submitter: Connie Wang

Submission Date: April 24, 2018, 8:23 p.m.

Version: 1

Publication Details
Feng YQ;Sligar SG,Biochemistry (1991) Effect of heme binding on the structure and stability of Escherichia coli apocytochrome b562. PMID:1931945
Additional Information

Structure view and single mutant data analysis

Study data

No weblogo for data of varying length.
Colors: D E R H K S T N Q A V I L M F Y W C G P

Data Distribution

Studies with similar sequences (approximate matches)

Correlation with other assays (exact sequence matches)

Relevant UniProtKB Entries

Percent Identity Matching Chains Protein Accession Entry Name
100.0 Soluble cytochrome b562 P0ABE7 C562_ECOLX
97.7 Soluble cytochrome b562 P0ABE8 C562_ECO57
97.7 Soluble cytochrome b562 Q8CVG7 C562_ECOL6