Identification, purification, biochemical and mass spectrometric characterization of novel phycobiliproteins from a marine red alga, Centroceras clavulatum.

Phycobilisomes are light-harvesting protein complexes and are widely distributed in red algae and cyanobacteria. Each phycobilisome contains highly fluorescent protein components called phycobiliproteins. Based upon the distinct physiochemical properties, phycobiliproteins are classified as allophycocyanin, phycocyanin, phycoerythrin and phycoerythrocyanin. In the present study, we describe purification and structural characterization of a novel phycocyanin and phycoerythrin isolated from a marine red macroalga, Centroceras clavulatum. The absorbance and fluorescence studies indicated that the purified proteins belong to R-Phycocyanin (R-PC) and R-Phycoerythrin (R-PE). The single bands under native-polyacrylamide gel electrophoresis revealed the intact molecular weights of R-PC and R-PE as 110kDa and 250kDa. The polypeptide compositions of the two proteins were demonstrated by SDS-PAGE. The result showed that R-PC contains two bands at 17 and 21kDa and were identified as α and ß subunits through mass spectrometry based proteomics experiments. SDS-PAGE of R-PE showed three distinct bands at 18, 19 and 35kDa and was subsequently identified as α, ß and γ subunits. The near-complete amino acid sequences of α and ß subunits of R-PC and R-PE were derived from mass spectrometric data combined with Mascot software and multiple de novo sequencing tools followed by homology search and manual validation.

Identification and characterization of a library of surfactins and fengycins from a marine endophytic Bacillus sp.

An endophytic bacterial strain from a marine green alga, Ulva lactuca, was isolated and identified by 16S rRNA gene sequencing method. The bacterial isolate was found to secrete two major families of cyclic depsilipopeptides, surfactins, and fengycins. Sequencing of the isolated lipopeptides was carried out using the MSn data obtained from an electrospray ionization (ESI) ion trap mass spectrometer coupled to an HPLC system. The assigned sequences were confirmed by a chemical derivatization approach involving esterification followed by mass spectrometric analysis. Distinction of leucine residues from isoleucine was established through a combined electron transfer dissociation-collision-induced dissociation (ETD-CID) method. The fengycins described in this study were found to cause significant delay of growth of two plants, Vigna radiata (mung bean) and Oryza sativa (rice). To the best of our knowledge, this is the first study describing identification and characterization of cyclic peptides from an endophytic Bacillus sp. isolated from marine algae.