Identification of multiple substrate binding sites in SLC4 transporters in the outward-facing conformation: Insights into the transport mechanism.

Solute carrier family 4 (SLC4) transporters mediate the transmembrane transport of HCO3-, CO32-, and Cl- necessary for pH regulation, transepithelial H+/base transport, and ion homeostasis. Substrate transport with varying stoichiometry and specificity is achieved through an exchange mechanism and/or through coupling of the uptake of anionic substrates to typically co-transported Na+. Recently solved outward-facing structures of two SLC4 members (human anion exchanger 1 [hAE1] and human electrogenic sodium bicarbonate cotransporter 1 [hNBCe1]) with different transport modes (Cl-/HCO3- exchange versus Na+-CO32- symport) revealed highly conserved three-dimensional organization of their transmembrane domains. However, the exact location of the ion binding sites and their protein-ion coordination motifs are still unclear. In the present work, we combined site identification by ligand competitive saturation mapping and extensive molecular dynamics sampling with functional mutagenesis studies which led to the identification of two substrate binding sites (entry and central) in the outward-facing states of hAE1 and hNBCe1. Mutation of residues in the identified binding sites led to impaired transport in both proteins. We also showed that R730 in hAE1 is crucial for anion binding in both entry and central sites, whereas in hNBCe1, a Na+ acts as an anchor for CO32- binding to the central site. Additionally, protonation of the central acidic residues (E681 in hAE1 and D754 in hNBCe1) alters the ion dynamics in the permeation cavity and may contribute to the transport mode differences in SLC4 proteins. These results provide a basis for understanding the functional differences between hAE1 and hNBCe1 and may facilitate potential drug development for diseases such as proximal and distal renal tubular acidosis.

An observational study to assess an electronic point-of-care wound documentation and reporting system regarding user satisfaction and potential for improved care.

The integration of information technology into daily patient care potentially provides a means to standardize care and enable continuous quality improvement through improved communication among care teams. A 2-month observational study was conducted on 38 residents with pressure ulcers at a 51-bed skilled nursing facility to rate the Ease of Use and Wound Management Effectiveness of a point-of-care electronic wound documentation system. Nine nurses evaluated the use of handheld "smart phone" devices equipped with a digital camera to document pressure ulcer assessment and treatment at point of care. Ease of Use (five items) was scored on a 5-point Likert scale (5 = very easy); Wound Management Effectiveness (eight items) was scored on a 5-point Likert scale (5 = very effective). Statistically significant mean changes in nurses' ratings were found for baseline compared to 2-month follow-up by paired t-test. Ease of Use ratings across the five criteria increased from an overall mean of 3.3 at baseline to 4.7 at follow-up (P = 0.5), while Wound Management Effectiveness increased from an overall mean of 3.3 at baseline to 4.4 at follow-up (P = 0.5) . The greatest gains for single items were reviewing wound progress (mean difference = 2.35; P = 0.000) and recognizing changes in wound status (mean difference = 1.78; P = 0.001) within the Ease of Use and Wound Management Effectiveness scales, respectively. The smallest change occurred in reading charts and notes (mean difference = 0.89) and ability to determine resident's risk level (mean difference = 0.39). Further research is needed to assess use of a wound documentation system in this and other settings, as well as to ascertain validity and reliability.