Cells, and the organelles within them, are surrounded by lipid-bilayer membranes that compartmentalize biochemical reactions
and pathways. Membrane-embedded proteins control the flux of molecules, energy, and information such that the segregated compartments
function as a unified living cell. Traditionally, membrane proteins were pictured as floating around quite independently of
the surrounding lipids, yet when this fluid-mosaic model was described, Singer and Nicolson qualified that “a small fraction
of the lipid may interact specifically with the membrane proteins” (1). It has taken 40 years to fully appreciate the importance of this assertion. On page 380 of this issue, Zhou et al. (2) report mass spectrometry of intact integral membrane protein complexes solubilized from bilayers. The results show that
specific structural lipids remain bound in the gas phase and can be counted.
"Biological membranes are highly organized proteolipid domains and there is increasing evidence of fine-scale organization into microdomains (Whitelegge, 2011; Holthuis and Ungermann, 2013). These comprise localized assemblies of specific proteins and lipids and are important in the spatial and temporal control of membrane protein complex assembly and regulation. "
[Show abstract][Hide abstract] ABSTRACT: The band-7 protein family comprises a diverse set of membrane-bound proteins characterized by the presence of a conserved domain. The exact function of this band-7 domain remains elusive, but examples from animal and bacterial stomatin-type proteins demonstrate binding to lipids and the ability to assemble into membrane-bound oligomers that form putative scaffolds. Some members, such as prohibitins (PHB) and human stomatin-like protein 2 (HsSLP2), localize to the mitochondrial inner membrane where they function in cristae formation and hyperfusion. In Arabidopsis, the band-7 protein family has diversified and includes plant-specific members. Mitochondrial-localized members include prohibitins (AtPHBs) and two stomatin-like proteins (AtSLP1 and -2). Studies into PHB function in plants have demonstrated an involvement in root meristem proliferation and putative scaffold formation for mAAA proteases, but it remains unknown how these roles are achieved at the molecular level. In this minireview we summarize the current status of band-7 protein functions in Arabidopsis, and speculate how the mitochondrial members might recruit specific lipids to form microdomains that could shape the organization and functioning of the respiratory chain.
[Show abstract][Hide abstract] ABSTRACT: Integral membrane proteins reside within the bilayer membranes that surround cells and organelles, playing critical roles in movement of molecules across them and the transduction of energy and signals. While their extreme amphipathicity presents technical challenges, biological mass spectrometry has been applied to all aspects of membrane protein chemistry and biology, including analysis of primary, secondary, tertiary and quaternary structure, as well as the dynamics that accompany functional cycles and catalysis.
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