Structures of apomyoglobin's various acid-destabilized forms.

Area of Science:

• Protein folding and biophysics
• Structural biology
• Biochemistry

Background:

• Horse heart apomyoglobin (apoMb) is a model protein for studying folding pathways.
• Destabilized states of apoMb, such as E and I forms, provide insights into early folding intermediates.
• Understanding these states is crucial for elucidating the protein folding energy landscape.

Purpose of the Study:

• To investigate the structures and melting thermodynamics of acid- and salt-destabilized states of horse heart apomyoglobin (apoMb).
• To characterize the tertiary and secondary structural features of the E and I forms.
• To relate these structural features to early events in the protein's folding pathway.

Main Methods:

• Studied apoMb using tryptophan fluorescence and FTIR spectroscopy to probe tertiary structure.
• Utilized far-UV CD and FTIR spectroscopy to assess secondary structure.
• Analyzed cooperative melting thermodynamics of different apoMb forms.

Main Results:

• Identified distinct acid- and salt-destabilized E and I forms of apoMb, resembling early folding structures.
• Both E and I forms retain a cooperative melting AGH core.
• The E form, a heterogeneous mixture of conformations, shows "random" backbone structures that convert to alpha-helix in the I forms, indicating different tertiary and secondary structures.

Conclusions:

• The E and I forms of apoMb possess distinct melting thermodynamics and structural properties.
• The E form's heterogeneity and the conversion to alpha-helix in I forms provide insights into early protein folding events.
• These findings contribute to understanding the energy landscape and structural features of apomyoglobin folding.