title: Folding and stability studies on C-PE and its natural N-terminal truncant.
abstract: The conformational and functional state of biliproteins can be determined by optical properties of the covalently linked chromophores. α-Subunit of most of the phycoerythrin contains 164 residues. Recently determined crystal structure of the naturally truncated form of α-subunit of cyanobacterial phycoerythrin (Tr-αC-PE) lacks 31 N-terminal residues present in its full length form (FL-αC-PE). This provides an opportunity to investigate the structure-function relationship between these two natural forms. We measured guanidinium chloride (GdmCl)-induced denaturation curves of FL-αC-PE and Tr-αC-PE proteins, followed by observing changes in absorbance at 565nm, fluorescence at 350 and 573nm, and circular dichroism at 222nm. The denaturation curve of each protein was analyzed for ΔGD(∘), the value of Gibbs free energy change on denaturation (ΔGD) in the absence of GdmCl. The main conclusions of the this study are: (i) GdmCl-induced denaturation (native state↔denatured state) of FL-αC-PE and Tr-αC-PE is reversible and follows a two-state mechanism, (ii) FL-αC-PE is 1.4kcalmol(-1) more stable than Tr-αC-PE, (iii) truncation of 31-residue long fragment that contains two α-helices, does not alter the 3-D structure of the remaining protein polypeptide chain, protein-chromophore interaction, and (iv) amino acid sequence of Tr-αC-PE determines the functional structure of the phycoerythrin.
authors.affiliation: Centre for Interdisciplinary Research in Basic Sciences, Jamia Millia Islamia (Central University), Jamia Nagar, New Delhi 110 025, India.
authors.forename: Khalid
authors.initials: K
authors.lastname: Anwer
authors.affiliation: BRD School of Biosciences, Sardar Patel University, Vallabh Vidyanagar, Gujarat 388 120, India.
authors.forename: Asha
authors.initials: A
authors.lastname: Parmar
authors.affiliation: Centre for Interdisciplinary Research in Basic Sciences, Jamia Millia Islamia (Central University), Jamia Nagar, New Delhi 110 025, India.
authors.forename: Safikur
authors.initials: S
authors.lastname: Rahman
authors.affiliation: BRD School of Biosciences, Sardar Patel University, Vallabh Vidyanagar, Gujarat 388 120, India.
authors.forename: Avani
authors.initials: A
authors.lastname: Kaushal
authors.affiliation: BRD School of Biosciences, Sardar Patel University, Vallabh Vidyanagar, Gujarat 388 120, India.
authors.forename: Datta
authors.initials: D
authors.lastname: Madamwar
authors.affiliation: Centre for Interdisciplinary Research in Basic Sciences, Jamia Millia Islamia (Central University), Jamia Nagar, New Delhi 110 025, India.
authors.forename: Asimul
authors.initials: A
authors.lastname: Islam
authors.affiliation: Centre for Interdisciplinary Research in Basic Sciences, Jamia Millia Islamia (Central University), Jamia Nagar, New Delhi 110 025, India. Electronic address: mihassan@jmi.ac.in.
authors.forename: Md Imtaiyaz
authors.initials: MI
authors.lastname: Hassan
authors.affiliation: Centre for Interdisciplinary Research in Basic Sciences, Jamia Millia Islamia (Central University), Jamia Nagar, New Delhi 110 025, India.
authors.forename: Faizan
authors.initials: F
authors.lastname: Ahmad
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry*; D000458:Cyanobacteria / Q000737:chemistry*; D019791:Guanidine / Q000737:chemistry; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010799:Phycoerythrin / Q000737:chemistry*; D011487:Protein Conformation; D011489:Protein Denaturation; D017510:Protein Folding; D017433:Protein Structure, Secondary; D021122:Protein Subunits / Q000737:chemistry; D016415:Sequence Alignment; D013816:Thermodynamics
chemical_list: D001426:Bacterial Proteins; D021122:Protein Subunits; D010799:Phycoerythrin; D019791:Guanidine
keywords: Biliproteins; C-phycoerythrin; Chromophore; Folding and stability; Protein denaturation