Substrate Specificity of Nickel/Cobalt Permeases: Insights from Mutants Altered in Transmembrane Domains I and II

HoxN, a high-affinity, nickel-specific permease of Ralstonia eutropha H16, and NhlF, a nickel/cobalt permease of Rhodococcus rhodochrous J1, are structurally related members of the nickel/cobalt transporter (NiCoT) family. These transporters have an eight-helix structure and are characterized by highly conserved segments with polar or charged amino acid residues in transmembrane domains (TMDs) II, III, V, and VI. Two histidine residues in a Ni(2+) binding motif, the signature sequence of NiCoTs, in TMD II of HoxN have been shown to be crucial for activity. Replacement of the corresponding His residues in NhlF affected both Co(2+) and Ni(2+) uptake, demonstrating that NhlF employs a HoxN-like mechanism for transport of the two cations. Multiple alignments of bacterial NiCoT sequences identified a striking correlation between a hydrophobic residue (Val or Phe) in TMD II and a position in the center of TMD I occupied by either an Asn (as in HoxN) or a His (as in NhlF). Introducing an isoleucine residue at the latter position strongly reduced HoxN activity and abolished NhlF activity, suggesting that a Lewis base N-donor moiety is important. The Asn-to-His exchange had no effect on HoxN, whereas the converse replacement reduced NhlF-mediated Ni(2+) uptake significantly. Replacement of the entire TMD I of HoxN by the respective NhlF segment resulted in a chimera that transported Ni(2+) and Co(2+) with low capacity. The Val-to-Phe exchange in TMD II of HoxN led to a considerable rise in Ni(2+) uptake capacity and conferred to the variant the ability to transport Co(2+). NhlF activity dropped in response to the converse mutation. Our data predict that TMDs I and II in NiCoTs spatially interact to form a critical part of the selectivity filter. As seen for the V64F variant of HoxN, modification of this site can increase the velocity of transport and concomitantly reduce the specificity

Practical Typed Lazy Contracts

Until now there has been no support for specifying and enforcing contracts within a lazy functional program. That is a shame, because contracts consist of pre- and post-conditions for functions that go beyond the standard static types. This paper presents the design and implementation of a small, easy-to-use, purely functional contract library for Haskell, which, when a contract is violated, also provides more useful information than the classical blaming of one contract partner. From now on lazy functional languages can profit from the assurances in the development of correct programs that contracts provide

Prevalence and Correlates of Smoking and Readiness to Quit Smoking in People Living with HIV in Austria and Germany.

We aimed to investigate the prevalence and correlates of smoking in people living with HIV (PLWHIV) in Germany and Austria and their readiness to quit. A total of 447 consecutive patients with confirmed positive HIV status who were treated in different outpatient HIV centres in Austria and Germany were included. Nicotine dependence and stages of change were assessed by standardized questionnaires, and this was confirmed by measuring exhaled carbon monoxide. Prevalence of smoking was 49.4%. According to a multivariate logistic regression analysis, higher age (for each year of life OR = 0.96; 95% CI 0.92-1.00) and tertiary education level (OR = 0.43; 95% CI 0.15-0.79) were associated with a lower chance, and occasional (OR = 3.75; 95% CI 1.74-8.07) and daily smoking of the partner (OR 8.78; 95% CI 4.49-17.17) were significantly associated with a higher chance of smoking. Moderate (OR = 3.41; 95% CI = 1.30-9.05) and higher nicotine dependency level (OR = 3.40; 95% CI 1.46-7.94), were significantly associated with higher chance, and older age (for each year of life OR = 0.95; 95% CI = 0.91-0.99), with lower chance for readiness to quit smoking. Those results may be used to address preventive measures to quit smoking aimed at PLWHIV and the importance of addressing smoking habits

Sociodemographic and medical data of smokers and non-smokers.

<p>Sociodemographic and medical data of smokers and non-smokers.</p

Smoking characteristics of participants who smoke (N = 221).

<p>Smoking characteristics of participants who smoke (N = 221).</p

Multivariate logistic regression model of characteristics associated with readiness to stop smoking among current smokers (N = 221).

<p>Multivariate logistic regression model of characteristics associated with readiness to stop smoking among current smokers (N = 221).</p