Three novel proteins co-localise with polyhydroxybutyrate (PHB) granules in Rhodospirillum rubrum S1

Abstract

Polyhydroxybutyrate (PHB), a biodegradable polymer accumulated by bacteria is deposited intracellularly in the form of inclusion bodies often called granules. The granules are supramolecular complexes harbouring a varied number of proteins on their surface, which have specific but incompletely characterised functions. By comparison with other organisms that produce biodegradable polymers, only two phasins have been described to date for Rhodosprillum rubrum, raising the possibility that more await discovery. Using a comparative proteomics strategy to compare the granules of wild-type R. rubrum with a PHB-negative mutant housing artificial PHB granules, we identified four potential PHB granules' associated proteins. These were: Q2RSI4, an uncharacterised protein; Q2RWU9, annotated as an extracellular solute-binding protein; Q2RQL4, annotated as basic membrane lipoprotein; and Q2RQ51, annotated as glucose-6-phosphate isomerase. In silico analysis revealed that Q2RSI4 harbours a Phasin_2 family domain and shares low identity with a single-strand DNA-binding protein from Sphaerochaeta coccoides. Fluorescence microscopy found that three proteins Q2RSI4, Q2EWU9 and Q2RQL4 co-localised with PHB granules. This work adds three potential new granule associated proteins to the repertoire of factors involved in bacterial storage granule formation, and confirms that proteomics screens are an effective strategy for discovery of novel granule associated proteins.

Photoheterotrophic Assimilation of Valerate and Associated Polyhydroxyalkanoate Production by Rhodospirillum rubrum

“…The second phasin (Rru_A3283) was found to be twice more abundant in the presence of valerate than under the succinate condition (fold change, 2.06; P ϭ 0.027; 80 peptides). We also highlighted the higher abundance of the uncharacterized protein Rru_A2111 (fold change, 3.56; P ϭ 2.24E-06; 27 peptides) which was recently described as a potential phasin by Narancic et al (38). Nevertheless, the exact role of these proteins remains unclear since they exhibit both a function in PHB granule mobilization and a role in increasing the number of PHB granules in a cell (39).…”

Phasin interactome reveals the interplay ofPhaFwith the polyhydroxyalkanoate transcriptional regulatory proteinPhaDinPseudomonas putida

“…Previous studies to determine the PHA granule proteome in other organisms suggested that a high number of proteins detected were experimental artefacts from the granule isolation procedure (Jendrossek and Pfeiffer, 2014; Sznajder et al ., 2015; Narancic et al ., 2018). In fact, a number of dubious proteins were detected in our study using either of the granule isolation methodologies employed.…”

The protective role of PHB and its degradation products against stress situations in bacteria

“…These 16 PGAPs constitute the PHB proteome in R. eutropha, representing highly organized multifunctional units (carbonosomes) (Jendrossek 2009;Jendrossek and Pfeiffer 2014) (Figure 1). Identification of proteins attached to PHB granules of other species of bacteria suggest that even more PGAPs might be associated with PHB granules (Tirapelle et al 2013;Narancic et al 2018;Moreno et al 2019). The PHA granules of mcl-PHA accumulating species have a similar structure consisting of a polymer core and several polymer surface-attached proteins.…”