In even the simplest of organisms, the complexity of its proteomic amalgam is compounded by the broad concentration range over which proteins are expressed, frequently spanning over nine orders of magnitude, as well as an undeterminable number of possible posttranslational modifications that can produce multiple isoforms of many proteins. Hence, neither genomics nor transcriptomics can realistically predict the constituency of the proteomic complement. For instance, there are 3778 distinct genes encoding for proteins that comprise the human plasma proteome, of which at least 51% of these genes encode more than one protein isoform. Consider the variable regions of the immunoglobulins, which collectively are expected to contribute nearly 10 million unique protein sequences to the total number of plasma proteins. Moreover, the search for biologically important proteins of low abundance is further impeded by the enormous range of protein concentrations, as exemplified in human plasma where the mass of albumin is nearly 10 billion times greater than that of important cell-signaling proteins like the interleukins. The diversity of proteins, ranging from very soluble proteins in biological fluids to extremely hydrophobic ones that exist either embedded in lipid membranes or as insoluble aggregates, suggests that the total protein constituency of cells may not be isolated without bias towards or against some protein subpopulations. On the other hand, the complexity of proteomes might be decreased by exploiting the bias toward specific protein subpopulations.

We invite investigators to contribute original research articles as well as review articles on the proteomic aspects of sample preparation, preservation, and fractionation. Potential topics include, but are not limited to:

• Affinity enrichment of low-abundance proteins and the depletion of high-abundance proteins
• Isolation and quantification of membrane proteins
• Preservation and quantification of rare posttranslational modifications of proteins
• Preservation of in vivo phosphorylation states
• Preparative and analytical scale sample fractionation strategies
• New sample preparation technologies
• Meeting the challenges of particularly difficult or labile samples and proteins
• Deep proteome research
• Challenges and advances in microbial proteomics sample preparation, fractionation, and analyses

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