Structure of the AAA protein Msp1 reveals mechanism of mislocalized membrane protein extraction.

The AAA protein Msp1 extracts mislocalized tail-anchored membrane proteins and targets them for degradation, thus maintaining proper cell organization. How Msp1 selects its substrates and firmly engages them during the energetically unfavorable extraction process remains a mystery. To address this question, we solved cryo-EM structures of Msp1-substrate complexes at near-atomic resolution. Akin to other AAA proteins, Msp1 forms hexameric spirals that translocate substrates through a central pore. A singular hydrophobic substrate recruitment site is exposed at the spiral's seam, which we propose positions the substrate for entry into the pore. There, a tight web of aromatic amino acids grips the substrate in a sequence-promiscuous, hydrophobic milieu. Elements at the intersubunit interfaces coordinate ATP hydrolysis with the subunits' positions in the spiral. We present a comprehensive model of Msp1's mechanism, which follows general architectural principles established for other AAA proteins yet specializes Msp1 for its unique role in membrane protein extraction

A rapid method for stereospecific glyceride analysis and its application to soybean and oat varieties

Rapid methods for the analysis of glyceride structure were explored so they could be applied to the determination of the extent of variation in glyceride structure of oilseed crops and possible use in oil crop breeding. For analysis of the sn-2-position of glycerol and the generation of diglycerides for stereospecific analysis, a method was adopted in which pancreatic lipase hydrolysis of the triglycerides and subsequent separation of the mono- and diglycerides was achieved on one thin layer silica gel plate;Attempts to phosphorylate diglycerides for stereospecific analysis of the glycerides on thin layer plates either with the enzyme diglyceride kinase or phenyldichlorophosphate were unsuccessful. But if the diglycerides were phosphorylated with phenyldichlorophosphate in a test tube, the phosphatide that were formed could be hydrolyzed with snake venom and the products separated on a single thin layer silica gel plate. These procedures made a reasonably rapid method possible;These methods were applied to a number of varieties and plant introductions of soybeans, Glycine max, and a closely related wild species, Glycine soya. A number of oat varieties, Avena sativa, and a closely related wild species, Avena sterilis, were also analyzed. The results were similar to those previously reported for soybeans and other oilseed plants. There was a linear relationship between the amount of a fatty acid on a particular position of glycerol and the amount of the fatty acid in the whole oil. Lines were fitted to the data by linear regression. None of the varieties and introductions tested varied widely from the linear relation. The plants deviating most from the linear relations need to be advanced a generation and retested to determine if the variation is genetic or environmental

A thermodynamic framework for modelling membrane transporters

Membrane transporters contribute to the regulation of the internal environment of cells by translocating substrates across cell membranes. Like all physical systems, the behaviour of membrane transporters is constrained by the laws of thermodynamics. However, many mathematical models of transporters, especially those incorporated into whole-cell models, are not thermodynamically consistent, leading to unrealistic behaviour. In this paper we use a physics-based modelling framework, in which the transfer of energy is explicitly accounted for, to develop thermodynamically consistent models of transporters. We then apply this methodology to model two specific transporters: the cardiac sarcoplasmic/endoplasmic Ca$^{2+}$ ATPase (SERCA) and the cardiac Na$^+$/K$^+$ ATPase