Structure and function of LCI1: a plasma membrane CO2 channel in the Chlamydomonas CO2 concentrating mechanism

Microalgae and cyanobacteria contribute roughly half of the global photosynthetic carbon assimilation. Faced with limited access to CO₂ in aquatic environments, which can vary daily or hourly, these microorganisms have evolved use of an efficient CO₂ concentrating mechanism (CCM) to accumulate high internal concentrations of inorganic carbon (C_i) to maintain photosynthetic performance. For eukaryotic algae, a combination of molecular, genetic and physiological studies using the model organism Chlamydomonas reinhardtii, have revealed the function and molecular characteristics of many CCM components, including active C_i uptake systems. Fundamental to eukaryotic C_i uptake systems are C_i transporters/channels located in membranes of various cell compartments, which together facilitate the movement of C_i from the environment into the chloroplast, where primary CO₂ assimilation occurs. Two putative plasma membrane C_i transporters, HLA3 and LCI1, are reportedly involved in active C_i uptake. Based on previous studies, HLA3 clearly plays a meaningful role in HCO₃^? transport, but the function of LCI1 has not yet been thoroughly investigated so remains somewhat obscure. Here we report a crystal structure of the full‐length LCI1 membrane protein to reveal LCI1 structural characteristics, as well as in vivo physiological studies in an LCI1 loss‐of‐function mutant to reveal the C_i species preference for LCI1. Together, these new studies demonstrate LCI1 plays an important role in active CO₂ uptake and that LCI1 likely functions as a plasma membrane CO₂ channel, possibly a gated channel.     

Hydrophilically enhanced 3-carboranyl thymidine analogues (3CTAs) for boron neutron capture therapy (BNCT) of cancer

Five novel 3-carboranyl thymidine analogues (3CTAs) were designed and synthesized for boron neutron capture therapy (BNCT) of cancer. Phosphorylation of all five 3CTAs was catalyzed by recombinant human thymidine kinase (hTK1) using adenosine triphosphate (ATP) as the phosphate donor. The obtained phosphorylation rates ranged from 4% to 64.5% relative to that of thymidine. The compound with the most favorable hTK1 binding properties had a k(cat)/K(M) value of 57.4% relative to that of thymidine and an IC(50) of inhibition of thymidine phosphorylation by hTK1 of 92 microM. Among the five synthesized 3CTAs, this agent had also the overall most favorable physicochemical properties. Therefore, it may have the potential to replace N5-2OH, the current lead 3CTA, in preclinical studies. An in silico model for the binding of this compound to hTK1 was developed.     

Peptidomimetics Through Click Chemistry: Synthesis of Novel β-Keto Triazole Acids from <Emphasis Type="Italic">N</Emphasis>-Protected Amino Acids

An efficient procedure for the preparation of azidomethylketones from N-urethane protected amino acids and their application in Cu(I) catalyzed azide-alkyne cycloaddition reaction are described. The synthesis has been carried out under mild conditions with all the commonly used urethane protected (Fmoc, Boc and Z) amino acids and the desired azides/triazoles were obtained in good yields. Incorporation of these triazole amino acids into small peptides generating dipeptidomimetics containing β-keto triazole units has also been demonstrated.     

Synthesis and antioxidant activity of 4-[2-(3,5-dimethoxyphenyl)ethenyl]-1,2-benzenediol, a metabolite of Sphaerophysa salsula

4-[2-(3,5-Dimethoxyphenyl)ethenyl]-1,2-benzenediol (7), a stilbene isolated from Sphaerophysa salsula, was synthesized from 3,4-dihydroxybenzaldehyde (1) in five steps in an overall yield of 33%. The spectral data for synthetic 7 are in good agreement with those of the natural product. Hydroxystilbene 7 showed potent antioxidative activity.     

Synthesis of Hybrid Peptidomimetics and Neoglycoconjugates Employing Click Protocol: Dual Utility of Poc-Group for Inserting Carbamate-Triazole Units into Peptide Backbone

Synthesis of new types of peptidomimetics and glycosylated amino acids possessing 1,2,3-triazole and carbamate moieties is described. Poc-protected amino acid esters/1-amino sugars were subjected to Cu(I) catalyzed [2+3]cycloaddition with desired azides under click protocol to obtain novel peptide and carbohydrate mimetics. The reaction is rapid, efficient and all the products are isolated in good yield and excellent purity.     

Inhibition of bladder overactivity by a combination of tibial neuromodulation and tramadol treatment in cats

Our recent study in cats revealed that inhibition of bladder overactivity by tibial nerve stimulation (TNS) depends on the activation of opioid receptors. TNS is a minimally invasive treatment for overactive bladder (OAB), but its efficacy is low. Tramadol (an opioid receptor agonist) is effective in treating OAB but elicits significant adverse effects. This study was to determine if a low dose of tramadol (expected to produce fewer adverse effects) can enhance the TNS inhibition of bladder overactivity. Bladder overactivity was induced in α-chloralose-anesthetized cats by an intravesical infusion of 0.25% acetic acid (AA) during repeated cystometrograms (CMGs). TNS (5 Hz) at two to four times the threshold intensity for inducing toe movement was applied during CMGs before and after tramadol (0.3-7 mg/kg iv) to examine the interaction between the two treatments. AA irritation significantly reduced bladder capacity to 24.8 ± 3.3% of the capacity measured during saline infusion. TNS alone reversibly inhibited bladder overactivity and significantly increased bladder capacity to 50-60% of the saline control capacity. Tramadol administered alone in low doses (0.3-1 mg/kg) did not significantly change bladder capacity, whereas larger doses (3-7 mg/kg) increased bladder capacity (50-60%). TNS in combination with tramadol (3-7 mg/kg) completely reversed the effect of AA. Tramadol also unmasked a prolonged (>2 h) TNS inhibition of bladder overactivity that persisted after termination of the stimulation. The results suggest a novel treatment strategy for OAB by combining tibial neuromodulation with a low dose of tramadol, which is minimally invasive with a potentially high efficacy and fewer adverse effects.     

“Thioureidopeptide”: Novel Synthon for the Synthesis of <Emphasis Type="Italic">N,N′, N″</Emphasis>-Trisubstituted Guanidinopeptide Mimics

The synthesis of N ^α-protected N,N′,N″-trisubstituted guanidinopeptide mimic molecules suitably decorated in peptide backbone has been delineated in one pot employing HgCl₂ as a desulphurizing agent. Chiral N ^α -protected thioureidopeptide esters were employed as synthons for the synthesis of title molecules. The protocol is simple and the reaction conditions employed were mild, amenable to the amino acid chemistry.