Texas non-donor-hospital project: a program to increase organ donation in community and rural hospitals.

Identifying and recovering donors from community and rural hospitals present a challenge to organ procurement organizations. A study of non-donor hospitals in the United States was undertaken at Johns Hopkins University, which identified 31 hospitals (in one service area) with the facilities to accommodate organ donation, though an organ donor had not been produced in 3 years. The purpose of this study was to determine whether donors could be produced from these hospitals. A large, geographically dispersed OPO initiated a program consisting of (1) in-house coordinators, and (2) routine notification of all hospital deaths. Following implementation of this program, organ donation increased 387% among the targeted 25 hospitals. The number of hospitals producing at least 1 organ donor increased 133%. The number of organs recovered in the project increased 449%. In-house coordinators, by identifying potential donors and facilitating an organ donor awareness program, can increase the number of organ donors in hospitals with low, but real, donor potential.

The ABC maltose transporter.

Bacterial ATP-binding cassette (ABC) transporters and their homologues in eukaryotic cells form one of the largest superfamilies known today. They function as primary pumps that couple substrate translocation across the cytoplasmic membrane to ATP hydrolysis. Although ABC transporters have been studied for more than three decades, the structure of these multi-component systems is unknown, and the mechanism of transport is not understood. This article reviews one of the most widely studied ABC systems, the maltose transporter of Escherichia coli. A first structural model of the transport channel allows discussion of possible mechanisms of transport. In addition, recent experimental evidence suggests that regulation of gene expression and transport activity is far more complex than expected.

Characterization of transmembrane domains 6, 7, and 8 of MalF by mutational analysis.

Oligonucleotide mutagenesis was used to isolate mutations in membrane-spanning segments 6, 7, and 8 of MalF. MalF is a cytoplasmic membrane component of the binding protein-dependent maltose transport system in Escherichia coli. The current structural model predicts eight transmembrane domains for MalF. Membrane-spanning segments 6, 7, and 8 of MalF flank or are part of the EAA-X3-G-X9-I-X-LP consensus region present in the cytoplasmic membrane subunits of the bacterial ABC transporter superfamily members. Mutations with two novel phenotypes with respect to substrate specificity of the maltose transport system were isolated. One mutant grew on minimal maltose media but not on media containing either maltoheptaose or maltoheptaose plus maltose and was thus termed dextrin dominant negative. The other class of mutations led to a maltose minus but maltoheptaose plus phenotype. Nine of the isolated mutations leading to changes in substrate specificity were tightly clustered on one face of the postulated transmembrane helix 6. A similar clustering of mutations was detected in transmembrane domain 7. The majority of mutations in membrane-spanning segment 7 led to a protease-sensitive or a conditional phenotype with respect to MalF function or both. Mutations in transmembrane domain 8 appeared to be more randomly distributed. The majority of mutations in membrane-spanning segment 8 caused a Mal+ Dex- phenotype. Six Mal+ suppressor mutations isolated to two mutations in transmembrane domain 7 changed amino acid residues in membrane-spanning segment 6 or 8.

Requirements for translocation of periplasmic domains in polytopic membrane proteins.

Periplasmic domains of cytoplasmic membrane proteins require export signals for proper translocation. These signals were studied by using a MalF-alkaline phosphatase fusion in a genetic selection that allowed the isolation of mislocalization mutants. In the original construct, alkaline phosphatase is fused to the second periplasmic domain of the membrane protein, and its activity is thus confined exclusively to the periplasm. Mutants that no longer translocated alkaline phosphatase were selected by complementation of a serB mutation. A total of 11 deletions in the amino terminus were isolated, all of which spanned at least the third transmembrane segment. This domain immediately precedes the periplasmic domain to which alkaline phosphatase was fused. Our results obtained in vivo support the model that amino-terminal membrane-spanning segments are required for translocation of large periplasmic domains. In addition, we found that the inability to export the alkaline phosphatase domain could be suppressed by a mutation, prlA4, in the secretion apparatus.