Biology Reference
In-Depth Information
3.3. Structural Similarities to Other Blue-Light-Responsive
Proteins
In addition to allowing the dissection of the roles of specific amino acids
in photoactivity and photoprotective function, the three-dimensional
structure of the OCP provides a basis for comparison to other well-
characterized photoactive proteins. The ability to respond to blue light
is not restricted to photosynthetic organisms, it is widespread in nature.
In the last decade, in addition to the emergence of understanding of
the OCP response to blue light, there have been tremendous advances
in understanding the structural basis of function in proteins that contain
blue-light-responsive BLUF (Blue light using flavin) and LOV (light oxy-
gen voltage) domains (reviewed in
Losi, 2007
). BLUF and LOV domains
typically function as receiver/input domains that can be either covalently
or noncovalently associated with various output domains for diverse func-
tions such as signal transduction, enzymatic activity or DNA binding
(
Losi, 2007
;
Nash, McNulty, et al., 2011
). There is a superficial structural
similarity between BLUF and LOV domains and the C-terminal domain
of the OCP: all contain a core beta sheet surrounded by helices. In BLUF
and LOV domains, changes in the chromophore in response to light cause
modifications of hydrogen bonding patterns among the helices and the
beta sheet and changes in exposure of discrete parts of the structure to
facilitate specific protein-protein interactions in response to the light sig-
nal. For example, in some LOV-based photoresponsive systems, light alters
the hydrogen bonding to the chromophore, which is propagated through
the beta sheet, culminating in the displacement of a helix (Jα) that other-
wise interacts effector domain (
Harper, Christie, et al., 2004
;
Harper, Neil,
et al., 2003
). Likewise, in many of these systems, structurally conserved
water molecules are also known to play a role in the conformational
changes that convert the light signal into an effector function.
4. THE OCP-PHYCOBILISOME INTERACTION
4.1. The
In Vitro
Reconstitution System: Only OCP
r
Interacts With Phycobilisomes
The recent development of an
in vitro
reconstitution system for the
OCP-related photoprotective mechanism provides new approaches to
the characterization of the OCP-phycobilisome interaction (
Gwizdala,
Wilson, et al., 2011
). When phycobilisomes are illuminated with strong
