CryoEM structures of anion exchanger 1 capture multiple states of inward- and outward-facing conformations.

Anion exchanger 1 (AE1, band 3) is a major membrane protein of red blood cells and plays a key role in acid-base homeostasis, urine acidification, red blood cell shape regulation, and removal of carbon dioxide during respiration. Though structures of the transmembrane domain (TMD) of three SLC4 transporters, including AE1, have been resolved previously in their outward-facing (OF) state, no mammalian SLC4 structure has been reported in the inward-facing (IF) conformation. Here we present the cryoEM structures of full-length bovine AE1 with its TMD captured in both IF and OF conformations. Remarkably, both IF-IF homodimers and IF-OF heterodimers were detected. The IF structures feature downward movement in the core domain with significant unexpected elongation of TM11. Molecular modeling and structure guided mutagenesis confirmed the functional significance of residues involved in TM11 elongation. Our data provide direct evidence for an elevator-like mechanism of ion transport by an SLC4 family member.

Cryo-EM structure of the sodium-driven chloride/bicarbonate exchanger NDCBE.

SLC4 transporters play significant roles in pH regulation and cellular sodium transport. The previously solved structures of the outward facing (OF) conformation for AE1 (SLC4A1) and NBCe1 (SLC4A4) transporters revealed an identical overall fold despite their different transport modes (chloride/bicarbonate exchange versus sodium-carbonate cotransport). However, the exact mechanism determining the different transport modes in the SLC4 family remains unknown. In this work, we report the cryo-EM 3.4 Å structure of the OF conformation of NDCBE (SLC4A8), which shares transport properties with both AE1 and NBCe1 by mediating the electroneutral exchange of sodium-carbonate with chloride. This structure features a fully resolved extracellular loop 3 and well-defined densities corresponding to sodium and carbonate ions in the tentative substrate binding pocket. Further, we combine computational modeling with functional studies to unravel the molecular determinants involved in NDCBE and SLC4 transport.

Rapid mobilization decreases length-of-stay in joint replacement patients.

BACKGROUND: Physiotherapy after total joint replacement enhances postoperative recovery. Implementing a pathway to include earlier postoperative mobilization can reduce the hospital length-of-stay as well as cost. QUESTIONS: Does a rapid rehabilitation program con- sisting of physical therapy on the day of surgery affect the hospital length-of-stay on patients undergoing either total hip or total knee replacements? Is there a difference in the effectiveness of rapid rehabilitation between patients under- going Total Hip and Total Knee Replacements? Can these patients tolerate day of surgery physical therapy sessions? PATIENTS AND METHODS: Nine-hundred hip and knee arthro- plasty patients were divided into two groups for analysis. Group 1 participated in a rapid rehabilitation physical therapy program that began with physical therapists in the recovery room. Group 2 received a standard physical therapy protocol starting the day after surgery. Progression with rehabilitation was followed, and length of hospital stay between the two groups was compared. RESULTS: Total length-of-stay was 3.9 days for the rapid rehabilitation group and was 4.4 days (p < 0.001) for the standard therapy group. We found the rapid rehabilitation group had a significantly shorter length-of-stay than patients who began therapy on postoperative day one. In addition to decreased length-of-stay, rapid rehabilitation also resulted in direct savings considering fewer hospital resources were utilized over the decreased time in-house. CONCLUSIONS: Rapid mobilization of total joint replacement patients in the recovery room can be accomplished safely and reduces the overall length of hospital stay for over 70 % of patients.