A novel suite of cyclotides from Viola odorata: sequence variation and the implications for structure, function and stability

Cyclotides are a fascinating family of plant-derived peptides characterized by their head-to-tail cyclized backbone and knotted arrangement of three disulfide bonds. This conserved structural architecture, termed the CCK (cyclic cystine knot), is responsible for their exceptional resistance to thermal, chemical and enzymatic degradation. Cyclotides have a variety of biological activities, but their insecticidal activities suggest that their primary function is in plant defence. In the present study, we determined the cyclotide content of the sweet violet Viola odorata, a member of the Violaceae family. We identified 30 cyclotides from the aerial parts and roots of this plant, 13 of which are novel sequences. The new sequences provide information about the natural diversity of cyclotides and the role of particular residues in defining structure and function. As many of the biological activities of cyclotides appear to be associated with membrane interactions, we used haemolytic activity as a marker of bioactivity for a selection of the new cyclotides. The new cyclotides were tested for their ability to resist proteolysis by a range of enzymes and, in common with other cyclotides, were completely resistant to trypsin, pepsin and thermolysin. The results show that while biological activity varies with the sequence, the proteolytic stability of the framework does not, and appears to be an inherent feature of the cyclotide framework. The structure of one of the new cyclotides, cycloviolacin O14, was determined and shown to contain the CCK motif. This study confirms that cyclotides may be regarded as a natural combinatorial template that displays a variety of peptide epitopes most likely targeted to a range of plant pests and pathogens.

The effect of non-standard employment on work-family balance

Across the last four decades, the structure of the Australian labour market has changed profoundly as non-standard forms of employment have become more prevalent. According to many researchers, the growth of non-standard work has been driven by employee preferences, particularly among married women, for greater flexibility to balance paid work with domestic responsibilities and other non-work related pursuits. In contrast, other researchers argue that the increasing prevalence of non-standard employment reflects employer demands for greater staffing flexibility. From this perspective, non-standard forms of employment are considered to have a negative effect on work-family balance. This paper explores whether non-standard employment is associated with improved or poorer work-to-family conflict and tests whether experiences vary by gender. It concentrates on three common forms of non-standard employment: part-time employment, casual and fixed-term work contracts and flexible scheduling practices (such as evening work, weekend work and irregular rostering). Analysis is based on 2299 employed parents from the first wave of the Household, Income and Labour Dynamics on Australia (HILDA) project. Results show that few scheduling measures are significant determinants of work-family balance. However, part-time employment is associated with reduced work-to-family strain for both men and women, even after controlling for various other employment and household related characteristics. Casual employment, in contrast, incurs the cost of poorer work-family balance for men. Surprisingly, HILDA data show that overall men experience greater work-to-family strain than women.