A comprehensive classification system for transmembrane molecular transporters has been developed and recently approved by the transport panel of the nomenclature committee of the International Union of Biochemistry and Molecular Biology. This system is based on (i) transporter class and subclass (mode of transport and energy coupling mechanism), (ii) protein phylogenetic family and subfamily, and (iii) substrate specificity. Almost all of the more than 250 identified families of transporters include members that function exclusively in transport. Channels (115 families), secondary active transporters (uniporters, symporters, and antiporters) (78 families), primary active transporters (23 families), group translocators (6 families), and transport proteins of ill-defined function or of unknown mechanism (51 families) constitute distinct categories. Transport mode and energy coupling prove to be relatively immutable characteristics and therefore provide primary bases for classification. Phylogenetic grouping reflects structure, function, mechanism, and often substrate specificity and therefore provides a reliable secondary basis for classification. Substrate specificity and polarity of transport prove to be more readily altered during evolutionary history and therefore provide a tertiary basis for classification. With very few exceptions, a phylogenetic family of transporters includes members that function by a single transport mode and energy coupling mechanism, although a variety of substrates may be transported, sometimes with either inwardly or outwardly directed polarity. In this review, I provide cross-referencing of well-characterized constituent transporters according to (i) transport mode, (ii) energy coupling mechanism, (iii) phylogenetic grouping, and (iv) substrates transported. The structural features and distribution of recognized family members throughout the living world are also evaluated. The tabulations should facilitate familial and functional assignments of newly sequenced transport proteins that will result from future genome sequencing projects.

https://mmbr.asm.org/content/mmbr/64/2/354.full.pdf

A Functional-Phylogenetic Classification System for Transmembrane Solute Transporters

Cardiac Na+,Ca2+ exchange is activated by a mechanism that requires hydrolysis of adenosine triphosphate (ATP) but is not mediated by protein kinases. In giant cardiac membrane patches, ATP acted to generate phosphatidylinositol-4,5-bisphosphate (PIP2) from phosphatidylinositol (PI). The action of ATP was abolished by a PI-specific phospholipase C (PLC) and recovered after addition of exogenous PI; it was reversed by a PIP2-specific PLC; and it was mimicked by exogenous PIP2. High concentrations of free Ca2+ (5 to 20 microM) accelerated reversal of the ATP effect, and PLC activity in myocyte membranes was activated with a similar Ca2+ dependence. Aluminum reversed the ATP effect by binding with high affinity to PIP2. ATP-inhibited potassium channels (KATP) were also sensitive to PIP2, whereas Na+,K+ pumps and Na+ channels were not. Thus, PIP2 may be an important regulator of both ion transporters and channels.

Regulation of Cardiac Na+,Ca2+ Exchange and KATP Potassium Channels by PIP2

Maps of epithermal- and fast-neutron fluxes measured by Lunar Prospector were used to search for deposits enriched in hydrogen at both lunar poles. Depressions in epithermal fluxes were observed close to permanently shaded areas at both poles. The peak depression at the North Pole is 4.6 percent below the average epithermal flux intensity at lower latitudes, and that at the South Pole is 3.0 percent below the low-latitude average. No measurable depression in fast neutrons is seen at either pole. These data are consistent with deposits of hydrogen in the form of water ice that are covered by as much as 40 centimeters of desiccated regolith within permanently shaded craters near both poles.

http://science.sciencemag.org/content/sci/281/5382/1496.full.pdf

Fluxes of fast and epithermal neutrons from Lunar Prospector: evidence for water ice at the lunar poles.

Regulation of transbilayer plasma membrane phospholipid asymmetry.

Technological developments, especially in mass spectrometry and bioinformatics, have revealed that living cells contain thousands rather than dozens of different lipids [for classification and nomenclature, see Fahy et al. ([Fahy et al., 2009][1])]. Now, the resulting questions are what is the

Lipid Map of the Mammalian Cell

During the Clementine 1 mission, a bistatic radar experiment measured the magnitude and polarization of the radar echo versus bistatic angle, beta, for selected lunar areas. Observations of the lunar south pole yield a same-sense polarization enhancement around beta = 0. Analysis shows that the observed enhancement is localized to the permanently shadowed regions of the lunar south pole. Radar observations of periodically solar-illuminated lunar surfaces, including the north pole, yielded no such enhancement. A probable explanation for these differences is the presence of low-loss volume scatterers, such as water ice, in the permanently shadowed region at the south pole.

https://science.sciencemag.org/content/sci/274/5292/1495.full.pdf

The Clementine Bistatic Radar Experiment

Mini-SAR: An Imaging Radar for the Chandrayaan 1 & Lunar Reconnaissance Orbiter Missions to the Moon

Newly processed Clementine bistatic radar data are co-registered with lunar polar illumination data, Arecibo ground-based monostatic radar data, and Lunar Prospector neutron spectrometer measurements. We find that Epithermal neutron flux anomalies are coincident with permanently shadowed regions at the lunar south pole and these areas also correlate with the ~=O Circular Polarization Ratio (CPR) enhancements revealed by processing of Clementine bistatic radar echoes obtained during lunar orbit 234, which in tum are co-located with areas of anomalous high CPR observed by Arecibo Observatory on the lower, sunshadowed wall of Shackleton crater. Additionally, Shackleton crater is located within a region identified as having an enhanced hydrogen content by the Lunar Prospector Neutron Spectrometer. Estimates of the extent of high CPR from Arecibo. Observatory and Clementine radar data independently suggest approximately 10 km of ice may be present on the inner Earth facing wall of Shackleton crater. None of the experiments that obtained the data presented here were ideally suited for definitively identifying ice in lunar polar regions. However, by assessing the relative merits of all available data we find that it is plausible that ice does occur in cold traps at the lunar south pole, and that future missions with instruments specifically designed to investigate these anomalies is worthy.

/pdf/integration-of-lunar-polar-datasets-3mk9v8zw6u.pdf

S. Nozette

Papers

The Clementine Bistatic Radar Experiment

Mini-SAR: An Imaging Radar for the Chandrayaan 1 & Lunar Reconnaissance Orbiter Missions to the Moon

Integration of Lunar Polar Datasets