Live imaging of collagen deposition during skin development and repair in a collagen I - GFP fusion transgenic zebrafish line.

Fibrillar collagen is a major component of many tissues but has been difficult to image in vivo using transgenic approaches because of problems associated with establishing cells and organisms that generate GFP-fusion collagens that can polymerise into functional fibrils. Here we have developed and characterised GFP and mCherry collagen-I fusion zebrafish lines with basal epidermal-specific expression. We use these lines to reveal the dynamic nature of collagen-I fibril deposition beneath the developing embryonic epidermis, as well as the repair of this collagen meshwork following wounding. Transmission electron microscope studies show that these transgenic lines faithfully reproduce the collagen ultrastructure present in wild type larval skin. During skin development we show that collagen I is deposited by basal epidermal cells initially in fine filaments that are largely randomly orientated but are subsequently aligned into a cross-hatch, orthogonal sub-epithelial network by embryonic day 4. Following skin wounding, we see that sub-epidermal collagen is re-established in the denuded domain, initially as randomly orientated wisps that subsequently become bonded to the undamaged collagen and aligned in a way that recapitulates developmental deposition of sub-epidermal collagen. Crossing our GFP-collagen line against one with tdTomato marking basal epidermal cell membranes reveals how much more rapidly wound re-epithelialisation occurs compared to the re-deposition of collagen beneath the healed epidermis. By use of other tissue specific drivers it will be possible to establish zebrafish lines to enable live imaging of collagen deposition and its remodelling in various other organs in health and disease.

Aryl azide photochemistry in defined protein environments.

A genetically encoded precursor to an aryl nitrene, para-azidophenylalanine, was introduced site specifically into proteins to deduce if distinct environments were capable of caging a reactive organic intermediate. Following photolysis of mutant T4 lysozyme or green fluorescent proteins, EPR spectra showed, respectively, the presence of a triplet nitrene and an anilino radical.

Regulation of beta-lactamase activity by remote binding of heme: functional coupling of unrelated proteins through domain insertion.

Coupling the activities of normally disparate proteins into one functional unit has significant potential in terms of constructing novel switching components for synthetic biology or as biosensors. It also provides a means of investigating the basis behind transmission of conformation events between remote sites that is integral to many biological processes, including allostery. Here we describe how the structures and functions of two normally unlinked proteins, namely, the heme binding capability of cytochrome b(562) and the antibiotic degrading beta-lactamase activity of TEM, have been coupled using a directed evolution domain insertion approach. The important small biomolecule heme directly modulates in vivo and in vitro the beta-lactamase activity of selected integral fusion proteins. The presence of heme decreased the concentration of ampicillin tolerated by Escherichia coli and the level of in vitro hydrolysis of nitrocefin by up to 2 orders of magnitude. Variants with the largest switching magnitudes contained insertions at second-shell sites that abut key catalytic residues. Spectrophotometry confirmed that heme bound to the integral fusion proteins in a manner similar to that of cytochrome b(562). Circular dichroism suggested that only subtle structural changes rather than gross folding-unfolding events were responsible for modulating beta-lactamase activity, and size exclusion chromatography confirmed that the integral fusion proteins remained monomeric in both the apo and holo forms. Thus, by sampling a variety of insertion positions and linker sequences, we are able to couple the functions of two unrelated proteins by domain insertion.