Unique contributions of an arginine side chain to ligand recognition in a glutamate-gated chloride channel

Glutamate recognition by neurotransmitter receptors often relies on Arg residues in the binding site, leading to the assumption that charge-charge interactions underlie ligand recognition. However, assessing the precise chemical contribution of Arg side chains to protein function and pharmacology has proven to be exceedingly difficult in such large and complex proteins. Using the in vivo nonsense suppression approach, we report the first successful incorporation of the isosteric, titratable Arg analog, canavanine, into a neurotransmitter receptor in a living cell, utilizing a glutamate-gated chloride channel from the nematode Haemonchus contortus. Our data unveil a surprisingly small contribution of charge at a conserved arginine side chain previously suggested to form a salt bridge with the ligand, glutamate. Instead, our data show that Arg contributes crucially to ligand sensitivity via a hydrogen bond network, where Arg interacts both with agonist and with a conserved Thr side chain within the receptor. Together, the data provide a new explanation for the reliance of neurotransmitter receptors on Arg side chains and highlight the exceptional capacity of unnatural amino acid incorporation for increasing our understanding of ligand recognition

Oxidative Modification of Tryptophan-Containing Peptides

We herein present a broadly useful method for the chemoselective modification of a wide range of tryptophan-containing peptides. Exposing a tryptophan-containing peptide to 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) resulted in a selective cyclodehydration between the peptide backbone and the indole side chain of tryptophan to form a fully conjugated indolyl-oxazole moiety. The modified peptides show a characteristic and significant emission maximum at 425 nm, thus making the method a useful strategy for fluorescence labeling

A Photolabile Linker for the Solid-Phase Synthesis of Peptide Hydrazides and Heterocycles

A photolabile hydrazine linker for the solid-phase synthesis of peptide hydrazides and hydrazine-derived heterocycles is presented. The developed protocols enable the efficient synthesis of structurally diverse peptide hydrazides derived from the standard amino acids, including those with side-chain protected residues at the C-terminal of the resulting peptide hydrazide, and are useful for the synthesis of dihydro­pyrano­[2,3-<i>c</i>]­pyrazoles. The linker is compatible with most commonly used coupling reagents and protecting groups for solid-phase peptide synthesis

Drivers of change in physical activity over 18 months in incident Parkinson’s disease

BACKGROUND AND AIM: Physical activity (PA) is important to maintain a healthy lifestyle. Beneficial effects of activity have been reported for people with Parkinson's disease (PD), and there is evidence to suggest it may be neuroprotective. Most people with PD do not achieve the recommended levels of PA, although the reasons for this are unclear [1]. It is important to understand the drivers of PA especially in the early stages of the disease before the secondary effects of PD are established. The aim of this study was to examine change in PA over 18 months in an incident cohort of PD and to identify possible drivers of PA. METHODS: For this preliminary analysis 35 people with PD [mean (SD) age 67.4 (10.4) years; 14 females; UPDRS III 23(10)] were recruited through an ongoing longitudinal study (ICICLE-PD). PA was measured for 7 days at baseline and 18 months, using a uniaxial accelerometer (ActivPal TM1,10Hz). PA outcomes included: 1) pattern of accumulation of activity (alpha); 2) number of steps accumulated in walking bouts of 100 steps (long); and 3) variability of stepping bout duration. A range of cognitive, motor, affective and quality of life outcomes were measured, including PD questionnaire (PDQ), the Geriatric Depression Scale (GDS), UPDRSIII and the Activities Balance Self- Confidence Scale (ABC). Multiple regression analysis was used to identify independent predictors of change in PA. RESULTS: At 18 months, there was a non-significant trend for people with PD to accumulate more steps in shorter bouts and fewer in longer bouts. Results from multiple regression showed that younger age, less severe PDQ stigma and lower PDQ mobility scores were independent predictors of a decrease in the number of steps accumulated in long bouts (F (5, 34) = 7.00, p < 0.001), with the model explaining 47% of the variance. In addition, more severe PDQ stigma and mobility scores were independent predictors of a decrease in steps accumulated in moderate bouts, total time spent walking and alpha. Post-hoc analysis showed these findings were independent of change in working status and medication. There were no significant independent predictors of change in variability of bout duration or number of steps accumulated in short bouts. CONCLUSION: Age, stigma and mobility are significant drivers of change in PA in early PD. This behavioural change reflects an early response to PD, even in those whose levels of physical activity should arguably be least affected. Future analysis will be performed on a larger cohort and compared with aged-matched controls to gain a greater understanding of the motor and non-motor drivers of PA in PD