Allosteric communication in the gating mechanism for controlled protein degradation by the bacterial ClpP peptidase.

Proteolysis is essential for the control of metabolic pathways and the cell cycle. Bacterial caseinolytic proteases (Clp) use peptidase components, such as ClpP, to degrade defective substrate proteins and to regulate cellular levels of stress-response proteins. To ensure selective degradation, access to the proteolytic chamber of the double-ring ClpP tetradecamer is controlled by a critical gating mechanism of the two axial pores. The binding of conserved loops of the Clp ATPase component of the protease or small molecules, such as acyldepsipeptide (ADEP), at peripheral ClpP ring sites, triggers axial pore opening through dramatic conformational transitions of flexible N-terminal loops between disordered conformations in the "closed" pore state and ordered hairpins in the "open" pore state. In this study, we probe the allosteric communication underlying these conformational changes by comparing residue-residue couplings in molecular dynamics simulations of each configuration. Both principal component and normal mode analyses highlight large-scale conformational changes in the N-terminal loop regions and smaller amplitude motions of the peptidase core. Community network analysis reveals a switch between intra- and inter-protomer coupling in the open-closed pore transition. Allosteric pathways that connect the ADEP binding sites to N-terminal loops are rewired in this transition, with shorter network paths in the open pore configuration supporting stronger intra- and inter-ring coupling. Structural perturbations, either through the removal of ADEP molecules or point mutations, alter the allosteric network to weaken the coupling.

Nurse-led rapid access vascular examination clinic triage reduces inappropriate referrals for peripheral arterial disease.

INTRODUCTION: Peripheral arterial disease causing intermittent claudication (IC) causes decreased quality of life and significant morbidity. We hypothesized that triage of patients referred with suspected IC at a nurse-led rapid access vascular examination (RAVE) clinic would identify those patients requiring vascular surgery assessment. METHODS: A prospective cohort study was performed. Patients referred with suspected IC were assessed using the Edinburgh claudication questionnaire (ECQ) and arterial Doppler assessment with segmental waveform analysis and calculation of ankle brachial pressure index (ABPI). Data were collected regarding cardiovascular risk and its modification. RESULTS: Of 451 consecutive patients, mean age was 65 years (range 30-89). Cardiovascular risk factors included: 173/451 (38%) current smokers (162/451 (36%) were ex-smokers); diabetes, 22%; hypertension, 46%; ischaemic heart disease (angina), 29%; dyslipidaemia, 27%. Therapeutic risk modifications included: antiplatelet therapy, 64.4%; lipid-lowering therapy, 57.8%. abnormal ABPI readings were present in 264/451 (59%), with ratio <0.9 in 209/451 (46.3%), >1.3 in 48/451 (10.6%), and incompressible vessels 7/451 (1.5%). Normal ABPI (ratio >0.9 and <1.3, triphasic Doppler waveforms) were found in 187/451 (41%), these patient were considered inappropriate referrals. Considering those patient with PAD diagnosed on abnormal ABPI (<0.9 or >1.3), Doppler waveform analysis was more sensitive and specific than ECQ. CONCLUSIONS: Diagnosis of IC with clinical history alone is inaccurate in 41 percent of cases, leading to inappropriate referral to vascular surgery. Doppler waveform analysis had excellent sensitivity and specificity for prediction of ABPI <0.9. ABPI measurement in primary care could result in a more efficient use of clinical resources.