title: Probing pH sensitivity of αC-phycoerythrin and its natural truncant: A comparative study.
abstract: Cyanobacterial phycoerythrin (αC-PE) from Phormidium tenue exists in two natural forms named as full length (FL-αC-PE) and truncated (Tr-αC-PE). FL-αC-PE and Tr-αC-PE are produced when cyanobacterium is grown in the optimal medium and nutrient deficient medium, respectively. Despite of N-terminal deletion, both proteins show similar spectroscopic properties. In this study, different optical properties of these two natural variants of C-PE were measured in the pH range 1.0-12.0 (1.0 ≤ pH ≤ 12.0). It was observed that: (i) their absorption, fluorescence and CD spectra remain unchanged within the range adjacent to neutral pH, 5.5-8.75, (ii) at pH values higher than 8.75 and lower than 5.5 their absorption, fluorescence and CD spectral signatures are changed significantly, and (iii) emission spectra of the covalently linked tetrapyrrole chromophores and Trp residue are perturbed at extreme pH values in the range 8.75<pH<5.5. Refolding experiments further suggest that pH-induced denaturation of both forms of C-PE is reversible in the pH range 2.5-11.0, but irreversible beyond this range on both sides of pH extremes. The pH-induced denaturation of both the full length and truncated αC-PEs follows a two-state mechanism.
authors.affiliation: Centre for Interdisciplinary Research in Basic Sciences, Jamia Millia Islamia (A Central University), Jamia Nagar, New Delhi 110 025, India.
authors.forename: Khalid
authors.initials: K
authors.lastname: Anwer
authors.affiliation: Centre for Interdisciplinary Research in Basic Sciences, Jamia Millia Islamia (A 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 388120, India.
authors.forename: Ravi R
authors.initials: RR
authors.lastname: Sonani
authors.affiliation: School of Chemistry and Chemical Engineering, Henan University of Technology, Henan 450001, China.
authors.forename: Faez Iqbal
authors.initials: FI
authors.lastname: Khan
authors.affiliation: Centre for Interdisciplinary Research in Basic Sciences, Jamia Millia Islamia (A Central University), Jamia Nagar, New Delhi 110 025, India.
authors.forename: Asimul
authors.initials: A
authors.lastname: Islam
authors.affiliation: BRD School of Biosciences, Sardar Patel University, Vallabh Vidyanagar, Gujarat 388120, India.
authors.forename: Datta
authors.initials: D
authors.lastname: Madamwar
authors.affiliation: Centre for Interdisciplinary Research in Basic Sciences, Jamia Millia Islamia (A Central University), Jamia Nagar, New Delhi 110 025, India.
authors.forename: Faizan
authors.initials: F
authors.lastname: Ahmad
authors.affiliation: Centre for Interdisciplinary Research in Basic Sciences, Jamia Millia Islamia (A 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
mesh_terms: D000458:Cyanobacteria / Q000201:enzymology; D006863:Hydrogen-Ion Concentration; D010446:Peptide Fragments / Q000737:chemistry*; D010799:Phycoerythrin / Q000737:chemistry*; D011487:Protein Conformation; D058849:Protein Refolding
chemical_list: D010446:Peptide Fragments; D010799:Phycoerythrin
keywords: C-phycoerythrin; Protein folding; pH-Induced denaturation