The radius of gyration of an apomyoglobin folding intermediate

Journal Article · Fri Oct 20 04:00:00 EDT 1995 · Science

DOI:https://doi.org/10.1126/science.270.5235.487· OSTI ID:183570

Eliezer, D; Jennings, P A; Wright, P E ^[1]

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1. Scripps Research Inst., LaJolla, CA (United States)

Apomyoglobin (apoMb) forms a stable compact partially folded state under acidic conditions. This {open_quotes}molten globule{close_quotes} intermediate is slightly expanded relative to the native form of the protein, with a radius of gyration (R{sub g}) of 23 ({plus_minus} 2) {Angstrom} versus 19 ({plus_minus}) {Angstrom}, and shows stable secondary structure in the A,G, and H helices. We demonstrated recently, with the use of stopped-flow circular dichroism and pulse-labeling hydrogen exchange measurements, that the earliest detectable intermediate (formed with 6 ms) in the apoMb kinetic refolding pathway closely resembles the equilibrium molten globule state populated under acid conditions. A key question remained as to how compact this kinetic intermediate is compared to the equilibrium and native states. The cooperative unfolding of the kinetic intermediate and the significant protection from amide proton exchange (as compared to corresponding isolated peptides in solution) led us to propose that the kinetic intermediate is also compact. Such a proposal could best be verified by direct determination of the size of the protein as it folds, but measurements of this nature were not feasible at the time. Newly developed improvements in time-resolved small angle x-ray scattering (SAXS) experiments allow direct measurement of the time-dependent change of R{sub g} of a protein as it folds in the millisecond to second time frame. We initiated studies of the refolding of apoMb using this technique, under conditions similar to those employed in our previous work. SAXS data collected during the first 100 ms after initiation of the refolding reaction are shown. 11 refs., 2 figs.

• Sponsoring Organization: USDOE
• OSTI ID: 183570
• Journal Information: Science, Journal Name: Science Journal Issue: 5235 Vol. 270; ISSN SCIEAS; ISSN 0036-8075
• Country of Publication: United States
• Language: English

Related Subjects

55 BIOLOGY AND MEDICINE
BASIC STUDIES
MOLECULAR STRUCTURE
MYOGLOBIN