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Cytokines regulate a variety of functions within the hematopoietic system, including proliferation, differentiation, suppression of apoptosis, and functional responses of cells (3,17,26,32). Many of these effects are mediated by cytokine interaction with receptors of the cytokine receptor superfamily. Although the cytokine receptors do not contain intrinsic kinase activity, they couple ligand binding to the induction of tyrosine phosphorylation, and this capability is essential for all functional responses (19,21,30,46). The Janus protein tyrosine kinases (Jaks) (18,20,21) are hypothesized to mediate these protein tyrosine phosphorylations on the basis of their association with one or more of the cytokine receptor subunits and activation of kinase activity following ligand binding. There are four Jaks, Jak1, Jak2, Jak3, and Tyk2, which variably associate with all of the known receptors of the cytokine receptor superfamily. In particular, the common ␤ chain of the interleukin-3 (IL-3) receptor associates with Jak2 (34), while the common ␥ chain of the IL-4 and IL-2 receptors associates with Jak3 (31) and the ligand-specific ␣ chain of the IL-4 receptor associates with Jak1.

Earth is flooded with plastics and the need for sustainable recycling strategies for polymers has become increasingly urgent. Enzyme‐based hydrolysis of post‐consumer plastic is an emerging strategy for closed‐loop recycling of polyethylene terephthalate (PET). The polyester hydrolase PHL7, isolated from a compost metagenome, completely hydrolyzes amorphous PET films, releasing 91 mg of terephthalic acid per hour and mg of enzyme. Vertical scanning interferometry shows degradation rates of the PET film of 6.8 μm h−1. Structural analysis indicates the importance of leucine at position 210 for the extraordinarily high PET‐hydrolyzing activity of PHL7. Within 24 h, 0.6 mgenzyme gPET−1 completely degrades post‐consumer thermoform PET packaging in an aqueous buffer at 70 °C without any energy‐intensive pretreatments. Terephthalic acid recovered from the enzymatic hydrolysate is then used to synthesize virgin PET, demonstrating the potential of polyester hydrolases as catalysts in sustainable PET recycling processes with a low carbon footprint.

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