Structures of apomyoglobin's various acid-destabilized forms.
The structures and the cold and hot melting thermodynamics of the acid- and salt-destabilized states of horse heart apomyoglobin (apoMb), including the E (extended) and various I forms, are studied using probes of tertiary structure (tryptophan fluorescence and FTIR spectroscopy) and secondary structure (far-UV CD and FTIR spectroscopy). These forms likely resemble early structures in the folding of the largely helical protein. Both the I and E forms retain the AGH core whereby the two ends of the protein are tied together with sufficient numbers of tertiary contacts, involving a number of hydrophobic residues, to show cooperative melting. The melting thermodynamics of E and I are distinctly different. E contains no other tertiary structure and probably little other secondary structure apart from the core. The more destabilized E form appears to contain "random" buried runs of polypeptide backbone which convert to alpha-helix in the I form(s). Most interestingly, E consists not of a single structure but is composed of a heterogeneous mixture of conformations, all showing corelike cooperative melting characteristics, and consisting presumably of varying contacts between the A portion of apomyoglobin and the G-H hairpin. These results bear on the energy landscape and structural features of the early part of apomyoglobin's folding pathway.
Gilmanshin
R
R
Department of Biochemistry, Albert Einstein College of Medicine, Bronx, New York 10461, USA.
Gulotta
M
M
Dyer
R B
RB
Callender
R H
RH
D000577:Amides; D000818:Animals; D000838:Anions / Q000737:chemistry; D001059:Apoproteins / Q000737:chemistry*; D002942:Circular Dichroism; D017666:Deuterium Oxide; D006736:Horses; D006863:Hydrogen-Ion Concentration; D009211:Myoglobin / Q000737:chemistry*; D009994:Osmolar Concentration; D017510:Protein Folding; D017433:Protein Structure, Secondary; D012965:Sodium Chloride / Q000737:chemistry; D012974:Sodium Iodide / Q000737:chemistry; D013050:Spectrometry, Fluorescence; D017550:Spectroscopy, Fourier Transform Infrared; D013816:Thermodynamics; D014364:Tryptophan / Q000737:chemistry
D000577:Amides; D000838:Anions; D001059:Apoproteins; D009211:Myoglobin; C010857:apomyoglobin; D012965:Sodium Chloride; D014364:Tryptophan; D012974:Sodium Iodide; D017666:Deuterium Oxide