Proteins play a crucial role in life, taking part in all vital processes in the body. In the past decade, there was increasing interest in delivering active forms of proteins to specific cells and organs. Intracellular protein delivery holds enormous promise for biological and medical applications, including cancer therapy, vaccination, regenerative medicine, treatment for loss-of-function genetic diseases and imaging. This tutorial review surveys recent developments in intracellular protein delivery using various nanocarriers. Methods such as lipid-mediated colloidal systems, polymeric nanocarriers, inorganic systems and protein-mediated carriers are reviewed. Advantages and limitations of current strategies, as well as future opportunities and challenges are also discussed.

Dissecting Megaenzyme Mechanisms: Filamentous fungi contain a class of multidomain enzymes, the highly-reducing iterative polyketide synthases (HR-IPKSs), which produce important natural products such as the cholesterol-lowering drug lovastatin. To produce their complex products, these megasynthases use multiple catalytic domains repeatedly in different combinations, but mechanistic details remain unclear. Ma et al. (p. 589 ) now report in vitro reconstitution of the complete catalytic function of lovastatin nonaketide synthase (LovB), the megasynthase that works together with a partner enzyme LovC to complete nearly 40 chemical steps required to construct the core of lovastatin. Analyses of the dependency of enzyme function on cofactors and on the partner enzyme elucidate the programming rules for this system.

Natural products and their derivatives play an important role in modern healthcare as frontline treatments for many diseases and as inspiration for chemically synthesized therapeutics. With advances in sequencing and recombinant DNA technology, many of the biosynthetic pathways responsible for the production of these chemically complex yet valuable compounds have been elucidated. With an ever-expanding toolkit of biosynthetic components, metabolic engineering is an increasingly powerful method to improve natural product titers and generate novel compounds. Heterologous production platforms have enabled access to pathways from difficult to culture strains, systems biology and metabolic modeling tools have resulted in increasing predictive and analytic capabilities, advances in expression systems and regulation have enabled the fine-tuning of pathways for increased efficiency, and characterization of individual pathway components has facilitated the construction of hybrid pathways for the production of new compounds. These advances in the many aspects of metabolic engineering not only have yielded fascinating scientific discoveries but also make it an increasingly viable approach for the optimization of natural product biosynthesis.