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The budding yeast Saccharomyces cerevisiae has historically been important in elucidating the various membrane trafficking events in eukaryotic cells. One of the defining moments in this field was the identification of conditional mutants in the secretory pathway, called sec mutants. This image of a sec1 mutant shows the typical accumulation of membranous vesicles in these strains. In this particular case, the accumulation of vesicles is due to a defect in docking and fusion of exocytic vesicles to the membrane. In an Elements piece in this issue (p 568), Randy Schekman shares his views of the membrane field 26 years later. Cover art by Erin Boyle based on imagery provided by Susan Hamamoto, Bob Lesch and Randy Schekman.
The difficulty in working with lipids and other membrane components has left many fundamental questions about the biochemistry of membranes unanswered. New techniques are required to determine how cell membranes are organized structurally and functionally.
Biological membranes are two-dimensional mixtures of an enormous number of different components. Modeling cell membranes as simple bilayer mixtures reveals rich phase behavior, but how can we use the observed phase behavior to understand the real membranes?
Physical chemistry explains the principles of self-organization of lipids into bilayers that form the matrix of biological membranes, and continuum theory of membrane energetics is successful in explaining many biological processes. With increasing sophistication of investigative tools, there is now a growing appreciation for lipid diversity and for the role of individual lipids and specific lipid-protein interactions in membrane structure and function.
As a pioneer in the field of membrane traffic, Randy Schekman shares a compelling historical perspective on the roles of various disciplines in forming a field and defining a scientist.
Understanding how cytokines interact with multimeric cell receptors to generate signals governing cell behavioral responses is crucial for the development of these promising pharmacological agents. A powerful quantitative approach is reported that was used to analyze the complicated case of binding of the GDNF family member artemin to the heteromeric GFRα3-Ret receptor.
Accumulating evidence indicates that protein S-nitrosylation may convey a broad spectrum of cellular signals. S-nitrosylation of critical cysteine thiols activates a subset of cation-permeable, transient receptor potential channel proteins (TRPs), which may represent a general mechanism for regulating stimulus-coupled cellular Ca2+ flux.
Ion-channel gating, or stochastic fluctuation between an open and a closed state, is not fully understood at the atomic level. Analysis of the bacterial channel OmpA now suggests that one mode of gating depends on the switching of a salt bridge within the pore.
A new pathway involving a fatty acid intermediate for the initiation of membrane phospholipid synthesis has been identified. This finding answers the question of how most bacteria catalyze the first acylation step in phosphatidic acid formation.