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Intimate interactions with carbonyl groups: dipole-dipole or n→π*?
Kimberli J Kamer1, Amit Choudhary, Ronald T Raines
1Department of Biochemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706, United States.
The Journal of Organic Chemistry
|November 21, 2012
Summary
Protein carbonyl groups interact via C═O···C═O and C-X···C═O bonds. These interactions, particularly short halogen···carbonyl contacts, exhibit n→π* signatures, suggesting they do not require a dipole for intimate protein interactions.
Area of Science:
- Structural Biology
- Chemical Physics
- Protein Science
Background:
- Amide carbonyl groups in proteins are known to participate in various non-covalent interactions.
- Previous hypotheses suggested these interactions, such as C═O···C═O and C-X···C═O, are primarily dipolar.
- Halogen atoms (X) can be involved in interactions with carbonyl groups.
Purpose of the Study:
- To investigate the nature of C-X···C═O interactions in protein crystal structures.
- To determine if dipolar interactions are essential for short halogen-carbonyl contacts.
- To explore the characteristics of these interactions, including preferred orientations and electronic signatures.
Main Methods:
- Survey of crystal structures containing short C-X···C═O contacts (within the sum of van der Waals radii).
- Analysis of the dihedral angles in structures with short C-X···C═O contacts.
- Examination of electronic signatures, specifically n→π* interactions, in short X(-)···C═O contacts.
Main Results:
- No preferred dihedral angle was observed for short C-X···C═O contacts.
- Short halogen···carbonyl contacts (X(-)···C═O) exhibit characteristics of n→π* interactions.
- The findings challenge the necessity of dipolar forces for intimate carbonyl group interactions.
Conclusions:
- Intimate interactions involving protein carbonyl groups do not exclusively rely on dipolar forces.
- The n→π* interaction is a significant factor in short-range halogen-carbonyl contacts.
- This study refines the understanding of non-covalent interactions in protein structures.
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