Enhancement of antibody fragment secretion into the Escherichia coli periplasm by co-expression with the peptidyl prolyl isomerase, FkpA, in the cytoplasm

Improper protein folding or aggregation can frequently be responsible for low expression and poor functional activity of antibody fragments secreted into the Escherichia coli periplasm. Expression issues also can affect selection of antibody candidates from phage libraries, since antibody fragments displayed on phage also are secreted into the E. coli periplasm. To improve secretion of properly folded antibody fragments into the periplasm, we have developed a novel approach that involves co-expressing the antibody fragments with the peptidyl prolyl cis-trans isomerase, FkpA, lacking its signal sequence (cytFkpA) which consequently is expressed in the E. coli cytosol. Cytoplasmic expression of cytFkpA improved secretion of functional Fab fragments into the periplasm, exceeding even the benefits from co-expressing Fab fragments with native, FkpA localized in the periplasm. In addition, panning and subsequent screening of large Fab and scFv naïve phage libraries in the presence of cytFkpA significantly increased the number of unique clones selected, as well as their functional expression levels and diversity.

A novel plant kinesin-related protein specifically associates with the phragmoplast organelles

In higher plants, the formation of the cell plate during cytokinesis requires coordinated microtubule (MT) reorganization and vesicle transport in the phragmoplast. MT-based kinesin motors are important players in both processes. To understand the mechanisms underlying plant cytokinesis, we have identified AtPAKRP2 (for Arabidopsis thaliana phragmoplast-associated kinesin-related protein 2). AtPAKRP2 is an ungrouped N-terminal motor kinesin. It first appeared in a punctate pattern among interzonal MTs during late anaphase. When the phragmoplast MT array appeared in a mirror pair, AtPAKRP2 became more concentrated near the division site, and additional signal could be detected elsewhere in the phragmoplast. In contrast, the previously identified AtPAKRP1 protein is associated specifically with bundles of MTs in the phragmoplast at or near their plus ends. Localization of the tobacco homolog(s) of AtPAKRP2 was altered by treatment of brefeldin A in BY-2 cells. We discuss the possibility that AtPAKRP1 plays a role in establishing and/or maintaining the phragmoplast MT array, and AtPAKRP2 may contribute to the transport of Golgi-derived vesicles in the phragmoplast.

A novel plant kinesin-related protein specifically associates with the phragmoplast organelles

In higher plants, the formation of the cell plate during cytokinesis requires coordinated microtubule (MT) reorganization and vesicle transport in the phragmoplast. MT-based kinesin motors are important players in both processes. To understand the mechanisms underlying plant cytokinesis, we have identified AtPAKRP2 (for Arabidopsis thaliana phragmoplast-associated kinesin-related protein 2). AtPAKRP2 is an ungrouped N-terminal motor kinesin. It first appeared in a punctate pattern among interzonal MTs during late anaphase. When the phragmoplast MT array appeared in a mirror pair, AtPAKRP2 became more concentrated near the division site, and additional signal could be detected elsewhere in the phragmoplast. In contrast, the previously identified AtPAKRP1 protein is associated specifically with bundles of MTs in the phragmoplast at or near their plus ends. Localization of the tobacco homolog(s) of AtPAKRP2 was altered by treatment of brefeldin A in BY-2 cells. We discuss the possibility that AtPAKRP1 plays a role in establishing and/or maintaining the phragmoplast MT array, and AtPAKRP2 may contribute to the transport of Golgi-derived vesicles in the phragmoplast.