An improved crystal structure of C-phycoerythrin from the marine cyanobacterium Phormidium sp. A09DM.

C-Phycoerythrin (PE) from Phormidium sp. A09DM has been crystallized using different conditions and its structure determined to atomic resolution (1.14 Å). In order for the pigment present, phycoerythrobilin (PEB), to function as an efficient light-harvesting molecule it must be held rigidly (Kupka and Scheer in Biochim Biophys Acta 1777:94-103, 2008) and, moreover, the different PEB molecules in PE must be arranged, relative to each other, so as to promote efficient energy transfer between them. This improved structure has allowed us to define in great detail the structure of the PEBs and their binding sites. These precise structural details will facilitate theoretical calculations of each PEB's spectroscopic properties. It was possible, however, to suggest a model for which chromophores contribute to the different regions of absorption spectrum and propose a tentative scheme for energy transfer. We show that some subtle differences in one of these PEB binding sites in two of the 12 subunits are caused by crystal contacts between neighboring hexamers in the crystal lattice. This explains some of the differences seen in previous lower resolution structures determined at two different pH values (Kumar et al. in Photosyn Res 129:17-28, 2016).

Biodegradation of poly(ester-urethane) coatings by Halopseudomonas formosensis.

Impranil® DLN-SD is a poly(ester-urethane) (PEU) that is widely used as coating material for textiles to fine-tune and improve their properties. Since coatings increase the complexity of such plastic materials, they can pose a hindrance for sustainable end-of-life solutions of plastics using enzymes or microorganisms. In this study, we isolated Halopseudomonas formosensis FZJ due to its ability to grow on Impranil DLN-SD and other PEUs as sole carbon sources. The isolated strain was exceptionally thermotolerant as it could degrade Impranil DLN-SD at up to 50°C. We identified several putative extracellular hydrolases of which the polyester hydrolase Hfor_PE-H showed substrate degradation of Impranil DLN-SD and thus was purified and characterized in detail. Hfor_PE-H showed moderate temperature stability (Tm = 53.9°C) and exhibited activity towards Impranil DLN-SD as well as polyethylene terephthalate. Moreover, we revealed the enzymatic release of monomers from Impranil DLN-SD by Hfor_PE-H using GC-ToF-MS and could decipher the associated metabolic pathways in H. formosensis FZJ. Overall, this study provides detailed insights into the microbial and enzymatic degradation of PEU coatings, thereby deepening our understanding of microbial coating degradation in both contained and natural environments. Moreover, the study highlights the relevance of the genus Halopseudomonas and especially the novel isolate and its enzymes for future bio-upcycling processes of coated plastic materials.

Structural basis for safe and efficient energy conversion in a respiratory supercomplex.

Proton-translocating respiratory complexes assemble into supercomplexes that are proposed to increase the efficiency of energy conversion and limit the production of harmful reactive oxygen species during aerobic cellular respiration. Cytochrome bc complexes and cytochrome aa3 oxidases are major drivers of the proton motive force that fuels ATP generation via respiration, but how wasteful electron- and proton transfer is controlled to enhance safety and efficiency in the context of supercomplexes is not known. Here, we address this question with the 2.8 Å resolution cryo-EM structure of the cytochrome bcc-aa3 (III2-IV2) supercomplex from the actinobacterium Corynebacterium glutamicum. Menaquinone, substrate mimics, lycopene, an unexpected Qc site, dioxygen, proton transfer routes, and conformational states of key protonable residues are resolved. Our results show how safe and efficient energy conversion is achieved in a respiratory supercomplex through controlled electron and proton transfer. The structure may guide the rational design of drugs against actinobacteria that cause diphtheria and tuberculosis.