Febs Letters

doi: 10.1002/1873-3468.13133pmid: N/A

Ganesan, Iniyan; Theg, Steven M.

doi: 10.1002/1873-3468.13342pmid: 30775779

Protein import into chloroplasts is carried out by the protein translocons at the outer and inner envelope membranes (TOC and TIC). Detailed structures for these translocons are lacking, with only a low‐resolution TOC complex structure available. Recently, we showed that the TOC/TIC translocons can import folded proteins, a rather unique feat for a coupled double membrane system. We also determined the maximum functional TOC/TIC pore size to be 30–35 Å. Here, we discuss how such large pores could form and compare the structural dynamics of the pore‐forming Toc75 subunit to its bacterial/mitochondrial Omp85 family homologs. We put forward structural models that can be empirically tested and also briefly review the pore dynamics of other protein translocons with known structures.

Mo, Tianlu; Yuan, Hong; Wang, Fangting; Ma, Suze; Wang, Jinxiu; Li, Ting; Liu, Guangfeng; Yu, Shaoning; Tan, Xiangshi; Ding, Wei; Zhang, Qi

doi: 10.1002/1873-3468.13341pmid: 30771247

S‐[(Z)‐2‐aminovinyl]‐d‐cysteine (AviCys) is a unique motif found in several classes of ribosomally synthesized and post‐translationally modified peptides (RiPPs). Biosynthesis of AviCys requires flavin‐dependent Cys decarboxylases, which are highly divergent among different RiPP classes. In this study, we solved the crystal structure of the cypemycin decarboxylase CypD. We show that CypD is structurally highly similar to lanthipeptide decarboxylases despite the absence of sequence similarities between them. We further show that Cys decarboxylases from four RiPP classes have evolved independently and form two major clusters. These results reveal the convergent evolution of AviCys biosynthesis and suggest that all the flavin‐dependent Cys decarboxylases likely have a similar Rossmann fold despite their sequence divergences.

Gudla, Ramurthy; Konduru, Guruprasad Varma; Nagarajaram, Hampapathalu Adimurty; Siddavattam, Dayananda

doi: 10.1002/1873-3468.13345pmid: 30791094

Our study aims to investigate the physiological role of organophosphate hydrolase (OPH), hitherto known for its involvement in the degradation of organophosphate insecticides and nerve agents in Sphingobium fuliginis. We find that OPH exists as part of the TonB‐dependent Transport system that is involved in nutrient transport across the bacterial outer membrane. OPH interacts physically with the Ton complex components ExbD and TonB. The surface‐exposed arginine residues (R91 and R96) of OPH facilitate its interaction with ExbD. OPH is targeted to the inner membrane of Escherichia coli only when it is co‐expressed with either ExbD or the ExbB/ExbD complex. In the absence of ExbD, OPH remains in the cytoplasm. Our findings suggest a role for OPH in outer membrane transport.

Karunakar, Pinreddy; Bhalla, Ameek; Sharma, Abhay

doi: 10.1002/1873-3468.13343pmid: 30779346

Intergenerational inheritance of transcriptional responses induced by low temperature rearing has recently been shown in Drosophila. Besides germline inheritance, fecal transfer experiments indirectly suggested that the acquired microbiome may also have contributed to the transcriptional responses in offspring. Here, we analyze expression data on inheritance of the cold‐induced effects in conjunction with previously reported transcriptomic differences between flies with a microbiota or axenic flies and provide support for a contribution of the acquired microbiome to the offspring phenotype. Also, based on a similar analysis in conjunction with diet‐ and metabolism‐related fly transcriptome data, we predicted and, then, experimentally confirmed that cold regulates triglyceride levels both inter‐ as well as trans‐generationally.

Acevedo, Claudia; Blanchard, Kris; Bacigalupo, Juan; Vergara, Cecilia

doi: 10.1002/1873-3468.13346pmid: 30801684

Odor transduction in the cilia of olfactory sensory neurons involves several ATP‐requiring enzymes. ATP is generated by glycolysis in the ciliary lumen, using glucose incorporated from surrounding mucus, and by oxidative phosphorylation in the dendrite. During prolonged stimulation, the cilia maintain ATP levels along their length, by unknown means. We used immunochemistry, RT‐PCR, and immunoblotting to explore possible underlying mechanisms. We found the ATP‐shuttles, adenylate and creatine kinases, capable of equilibrating ATP. We also investigated how glucose delivered by blood vessels in the olfactory mucosa reaches the mucus. We detected, in sustentacular and Bowman's gland cells, the crucial enzyme in glucose secretion glucose‐6‐phosphatase, implicating both cell types as putative glucose pathways. We propose a model accounting for both processes.

Wilson, Robert H.; Thieulin‐Pardo, Gabriel; Hartl, Franz‐Ulrich; Hayer‐Hartl, Manajit

doi: 10.1002/1873-3468.13352pmid: 30815863

Improving the performance of the key photosynthetic enzyme Ribulose‐1,5‐bisphosphate carboxylase/oxygenase (Rubisco) by protein engineering is a critical strategy for increasing crop yields. The extensive chaperone requirement of plant Rubisco for folding and assembly has long been an impediment to this goal. Production of plant Rubisco in Escherichia coli requires the coexpression of the chloroplast chaperonin and four assembly factors. Here, we demonstrate that simultaneous expression of Rubisco and chaperones from a T7 promotor produces high levels of functional enzyme. Expressing the small subunit of Rubisco with a C‐terminal hexahistidine‐tag further improved assembly, resulting in a ~ 12‐fold higher yield than the previously published procedure. The expression system described here provides a platform for the efficient production and engineering of plant Rubisco.

Biswas, Rupam; Singh, Bina Kumari; Dutta, Debajyoti; Das, Prabir Kumar; Maiti, Mrinal Kumar; Basak, Amit; Das, Amit Kumar

doi: 10.1002/1873-3468.13339pmid: 30847903

In Mycobacterium tuberculosis, acyl carrier protein (AcpM)‐mediated fatty acid synthase type II is integral for the synthesis of mycolic acids. AcpM, designated as an atypical ACP, comprises of a putative 33 amino acid long C‐terminal extension which is distinctive in nature. Here, we aimed at devising an ‘easy‐to‐go’ method for the generation of crypto‐AcpM loaded with a solvatochromic probe 7‐Nitrobenz‐2‐oxa‐1,3‐diazol‐4‐yl, which is linked to the 4′‐phosphopantetheine (Ppant) prosthetic group of AcpM. The crypto‐AcpM, coupled with fluorescence spectroscopy and molecular dynamics simulation studies, was employed to explore the elusive dynamics of Ppant arm in AcpM. This investigation establishes the role of the flexible C‐terminal extension of AcpM in regulating the prosthetic group sequestration ability by modulating the ‘Asp‐Ser‐Leu’ motif.

Ashokan, Anisha; Kameswaran, Mythili; Aradhyam, Gopala Krishna

doi: 10.1002/1873-3468.13344pmid: 30801688

The human APJ receptor (APJR), activated by apelin isoforms, regulates cardiovascular functions and fluid homeostasis. Understanding its structure‐function relationship is crucial for a comprehensive knowledge of signalling aberrations that cause several physiological disorders. Here, we demonstrate the influence of extracellular loop (ECL) domains in the mechanism of β‐arrestin‐mediated signalling from human APJR: Apelin system. Alanine mutations of evolutionarily conserved residues were characterized using receptor internalization, β‐arrestin pull‐down, Akt phosphorylation and cell migration assay. C281A and 268KTL270‐AAA in ECL3 were deficient in all assays, whereas 183MDYS186‐AAAA mutant in ECL2 showed impaired β‐arrestin‐mediated signalling but demonstrated Gi‐dependent cell migration. Our findings establish that conserved residues in the extracellular domain play a prominent role in modulating receptor interactions with the β‐arrestin signalling cascade.

Mazaki, Yuichi; Higashi, Tsunehito; Onodera, Yasuhito; Nam, Jin‐Min; Hashimoto, Ari; Hashimoto, Shigeru; Horinouchi, Takahiro; Miwa, Soichi

doi: 10.1002/1873-3468.13347pmid: 30801683

Endothelin (ET)‐1 is involved in the vascular system, cell proliferation and apoptosis. ET receptors consist of ET type A receptor (ETAR) and ET type B receptor (ETBR). ETAR and ETBR generally exhibit opposite responses, although many exceptions exist. In the present study, we attempted to identify ETAR‐ or ETBR‐specific binding proteins to understand the differences in ETAR‐ and ETBR‐mediated responses after ET‐1 stimulation. The 78‐kDa glucose‐regulated protein (GRP78) showed a stronger binding affinity towards ETBR than towards ETAR. Moreover, GRP78 overexpression promoted ETBR‐mediated ERK activation and GRP78 silencing suppressed ETBR‐mediated ERK activation. Furthermore, ETBR can localize GRP78 to the cell periphery. These results suggest that the interaction of ETBR with GRP78 affects ERK activation and GRP78 localization.