List Of Faculty

Khalid Anwera, Ravi Sonanib, Datta Madamwarb, Parvesh Singhc, Faez Khanc, Krishna
Bisettyc, Faizan Ahmada & Md. Imtaiyaz Hassana
a Centre for Interdisciplinary Research in Basic Sciences, Jamia Millia Islamia (A Central
University), Jamia Nagar, New Delhi 110 025, India
b BRD School of Biosciences, Sardar Patel University, Vallabh Vidyanagar, Gujarat 388 120,
India
c Department of Chemistry, Durban University of Technology, Durban 4000, South Africa

Abstract

The conformational state of biliproteins can be determined by optical properties of the covalently linked chromophores.
Recently determined crystal structure of truncated form of α-subunit of cyanobacterial phycoerythrin (αC-PE) from
Phormidium tenue provides a new insight into the structure–function relationship of αC-PE. To compare their stabilities,
we have measured urea-induced denaturation transitions of the full length αC-PE (FL-αC-PE) and truncated αC-PE
(Tr-αC-PE) followed by observing changes in absorbance at 565 nm, fluorescence at 350 and 573 nm, and circular
dichroism at 222 nm as a function of [urea], the molar concentration of urea. The transition curve of each protein was
analyzed for ΔGD
0, the value of Gibbs free energy change on denaturation (ΔGD) in the absence of urea; m, the slope
(=∂ΔGD/∂[urea]), and Cm, the midpoint of the denaturation curve, i.e. [urea] at which ΔGD = 0. A difference of about
10% in ΔGD
0 observed between FL-αC-PE and Tr-αC-PE, suggests that the two proteins are almost equally stable, and
the natural deletion of 31 residues from the N-terminal side of the full length protein does not alter its stability.
Furthermore, normalization of probes shows that the urea-induced denaturation of both the proteins is a two-state
process. Folding of both structural variants (Tr-αC-PE and FL-αC-PE) of P. tenue were also studied using molecular
dynamics simulations at 300 K. The results show clearly that the stability of the proteins is evenly distributed over the
whole structure indicating no significant role of N-terminal residues in the stability of both proteins.