Cellular localization of cytochrome bd in cyanobacteria using genetic code expansion

Electron transport in cyanobacterial thylakoid membranes: Are cyanobacteria simple models for photosynthetic organisms?

Cyanobacteria are structurally the simplest oxygenic phototrophs, which makes it difficult to understand the regulation of photosynthesis because the photosynthetic and respiratory processes share the same thylakoid membranes and cytosolic space. This review aimed to summarise the molecular mechanisms and in vivo activities of electron transport in cyanobacterial thylakoid membranes based on the latest progress in photosynthesis research in cyanobacteria. Photosynthetic linear electron transport for CO2 assimilation has the dominant electron flux in the thylakoid membranes. The capacity of O2 photoreduction in cyanobacteria is comparable to the photosynthetic CO2 assimilation, which is mediated by flavodiiron proteins. Additionally, cyanobacterial thylakoid membranes harbour the significant electron flux of respiratory electron transport through a homologue of respiratory complex I, which is also recognized as the part of cyclic electron transport chain if it is coupled with photosystem I in the light. Further, O2-independent alternative electron transports through hydrogenase and nitrate reductase function with reduced ferredoxin as the electron donor. Whereas all these electron transports are recently being understood one by one, the complexity as the whole regulatory system remains to be uncovered in near future.

Bioorthogonal PEGylation Prolongs the Elimination Half-Life of N-TIMP2 While Retaining MMP Inhibition

Tissue inhibitors of metalloproteinases (TIMPs) are natural inhibitors of the matrix metalloproteinase (MMP) family of proteins, whose members are key regulators of the proteolysis of extracellular matrix components and hence of multiple biological processes. In particular, imbalanced activity of matrix metalloproteinase-14 (MMP-14) may lead to the development of cancer and cardiovascular and other diseases. This study aimed to engineer TIMP2, one of the four homologous TIMPs, as a potential therapeutic by virtue of its ability to bind to the active-site Zn²⁺ of MMP-14. However, the susceptibility to degradation of TIMP2 and its small size, which results in a short circulation half-life, limit its use as a therapeutic. PEGylation was thus used to improve the pharmacokinetic profile of TIMP2. PEGylation of the MMP-targeting N-terminal domain of TIMP2 (N-TIMP2), via either cysteine or lysine residues, resulted in a significant decrease in N-TIMP2 affinity toward MMP-14 or multisite conjugation and conjugate heterogeneity, respectively. Our strategy designed to address this problem was based on incorporating a noncanonical amino acid (NCAA) into N-TIMP2 to enable site-specific mono-PEGylation. The first step was to incorporate the NCAA propargyl lysine (PrK) at position S31 in N-TIMP2, which does not interfere with the N-TIMP2-MMP-14 binding interface. Thereafter, site-specific PEGylation was achieved via a click chemistry reaction between N-TIMP2-S31PrK and PEG-azide-20K. Inhibition studies showed that PEGylated N-TIMP2-S31PrK did indeed retain its inhibitory activity toward MMP-14. The modified protein also showed improved serum stability vs non-PEGylated N-TIMP2. In vivo pharmacokinetic studies in mice revealed a significant 8-fold increase in the elimination half-life of PEGylated N-TIMP2 vs the non-PEGylated protein. This study shows that site-specific bioorthogonal mono-PEGylation extends the half-life of N-TIMP2 without impairing its biological activity, thereby highlighting the advantage of this strategy for generating potent PEGylated proteins.

An inside look at a biofilm: Pseudomonas aeruginosa flagella biotracking

The opportunistic pathogen, Pseudomonas aeruginosa, a flagellated bacterium, is one of the top model organisms for biofilm studies. To elucidate the location of bacterial flagella throughout the biofilm life cycle, we developed a new flagella biotracking tool. Bacterial flagella were site-specifically labeled via genetic code expansion. This enabled us to track bacterial flagella during biofilm maturation. Live flagella imaging revealed the presence and synthesis of flagella throughout the biofilm life cycle. To study the possible role of flagella in a biofilm, we produced a flagella knockout strain and compared its biofilm to that of the wild-type strain. Results showed a one order of magnitude stronger biofilm structure in the wild type in comparison with the flagella knockout strain. This suggests a possible structural role for flagella in a biofilm, conceivably as a scaffold. Our findings suggest a new model for biofilm maturation dynamic which underscores the importance of direct evidence from within the biofilm.

Genetic Code Expansion of Vibrio natriegens

Escherichia coli has been considered as the most used model bacteria in the majority of studies for several decades. However, a new, faster chassis for synthetic biology is emerging in the form of the fast-growing gram-negative bacterium Vibrio natriegens. Different methodologies, well established in E. coli, are currently being adapted for V. natriegens in the hope to enable a much faster platform for general molecular biology studies. Amongst the vast technologies available for E. coli, genetic code expansion, the incorporation of unnatural amino acids into proteins, serves as a robust tool for protein engineering and biorthogonal modifications. Here we designed and adapted the genetic code expansion methodology for V. natriegens and demonstrate an unnatural amino acid incorporation into a protein for the first time in this organism.