Domains in Proteins
Index to Course Material
Index to Section 10
Identification
References
DOMAIN MOVEMENTS
This section is largely based on the excellent review by
Gerstein et al. (1994). Mark Gerstein is also largely responsible for
The Protein Motions Database
Protein flexibility is demonstrated by large relative movements of
domains, for example, in aspartic proteinases the two lobes have large
relative shifts as identified by Sali et al., (1992).
Such motions are important for functions like catalysis,
ligand binding, regulation of activity, formation of protein
assemblies and transport of metabolites. Often the domains constitute
a binding site at the interface wherein closed conformations of
domains correspond to inactive form of the enzyme while open
conformations of domains correspond to the active form of the
enzyme, illustrating induced fit in recognition (Koshland, 1958).
Mechansisms of domain movements -
-
Intrinsic flexibility -
Several small movements in secondary structures which has a
cummulative effect. This may be further classified into two types:
- (a) movements not constrained by packing interactions like those
involving hinge motions in strands and helices. This may be slight
deformations in backbone torsion angles of strands/helices
(for example strand movements in lactoferrin,
helix deformation in lactate dehydrogenase from an alpha-helix to
3(10) helix (Gerstein & Chothia, 1991),
kinks involving prolines in helices as in adenylate kinase (Gerstein
et al., 1994),
interconversion of helix and extended conformations as in calmodulin
(Ikura et al. 1992) and in triglyceride lipase (Derewande et al., 1992)).
- (b) shear movements at the domain interface which are constrained by
packing interactions. The domain movements may be perpendicular or
parallel to the interface between the domains. If it is parallel, the
movements are largely due to small sidechain torsion angle changes often
within the same preferred ranges (for example domain movements in
citrate synthases (Remington et al., 1982) between the small and large
domains is by side chain movements in residues in pairs of packed helices).
An example of movements perpendicular to the domain interface is
observe in aspartyl aminotransferase (McPhalen et al., 1992).
- Hinged domain movements -
In order that each subunit in the tobacco bushy stunt virus fits into
the icosahedral symmetry, the S and P domains undergo displacements
mainly by the change in conformation of the peptide that forms a linker
between the two (Olsen et al., 1983). On the other hand in the transport
proteins like lactoferrin, the open and closed forms of the two domains
involve a 53 degree rotation which is achieved by two strands that
connect two domains (Anderson et al., 1990). More complex hinge motions
take place in protein kinase (Knighton et al., 1991) and in adenylate
kinases (Berry et al., 1994).
- Ball-and-socket motion -
The variable (light and heavy chain) domains of antibodies rotate about
50 degrees with respect to the heavy (light and heavy chain) by means
of a combination of hinge and shear motions (Lesk and Chothia, 1988).
R. Sowdhamini 1995
Index to Course Material
Index to Section 10
Identification
References
Last updated 11th Jun '96