Importance of Biopolymer Molecular Flexibility in Ultrafiltration Processes

Concentrating membrane proteins using ultrafiltration without concentrating detergents

Membrane proteins (MPs) are of rapidly growing interest in the design of pharmaceutical products, novel sensors, and synthetic membranes. Ultrafiltration (UF) using commercially available centrifugal concentrators is typically employed for laboratory-scale concentration of low-yield MPs, but its use is accompanied by a concomitant increase in concentration of detergent micelles. We present a detailed analysis of the hydrodynamic processes that control detergent passage during ultrafiltration of MPs and propose methods to optimize detergent passage during protein concentration in larger-scale membrane processes. Experiments were conducted using nonionic detergents, octyl-β-D glucoside (OG), and decyl-β-D maltoside (DM) with the bacterial water channel protein, Aquaporin Z (AqpZ) and the light driven chloride pump, halorhodopsin (HR), respectively. The observed sieving coefficient (So ), a measure of detergent passage, was evaluated in both stirred cell and centrifugal systems. So for DM and OG increased with increasing filtrate flux and decreasing shear rates in the stirred cell, that is, with increasing concentration polarization (CP). Similar effects were observed during filtration of MP-detergent (MPD) micelles. However, lower transmission was observed in the centrifugal system for both detergent and MPD systems. This is attributed to free convection-induced shear and hence reduced CP along the membrane surface during centrifugal UF. Thus to concentrate MPs without retention of detergent, design of UF systems that promote CP is required. Biotechnol. Bioeng. 2016;113: 2122-2130. © 2016 Wiley Periodicals, Inc.

Advances and trends in the design, analysis, and characterization of polymer-protein conjugates for "PEGylaided" bioprocesses

In addition to their use as therapeutics and because of their enhanced properties, PEGylated proteins have potential application in fields such as bioprocessing. However, the use of PEGylated conjugates to improve the performance of bioprocess has not been widely explored. This limited additional industrial use of PEG-protein conjugates can be attributed to the fact that PEGylation reactions, separation of the products, and final characterization of the structure and activity of the resulting species are not trivial tasks. The development of bioprocessing operations based on PEGylated proteins relies heavily in the use of analytical tools that must sometimes be adapted from the strategies used in pharmaceutical conjugate development. For instance, to evaluate conjugate performance in bioprocessing operations, both chromatographic and non-chromatographic steps must be used to separate and quantify the resulting reaction species. Characterization of the conjugates by mass spectrometry, circular dichroism, and specific activity assays, among other adapted techniques, is then required to evaluate the feasibility of using the conjugates in any operation. Correct selection of the technical and analytical methods in each of the steps from design of the PEGylation reaction to its final engineering application will ensure success in implementing a "PEGylaided" process. In this context, the objective of this review is to describe technological and analytical trends in developing successful applications of PEGylated conjugates in bioprocesses and to describe potential fields in which these proteins can be exploited.