The dual-specificity phosphatase (DUSP) 13 gene encodes two atypical DUSPs, DUSP13B/TMDP and DUSP13A/MDSP using alternative exons. DUSP13B protein is most highly expressed in testis, particularly in spermatocytes and round spermatids of the seminiferous tubules, while that of DUSP13A is restricted to skeletal muscle. Here, we show that DUSP13B inactivated MAPK activation in the order of selectivity, JNK = p38>ERK in cells, while DUSP13A did not show MAPK phosphatase activity. Reporter gene analysis showed that DUSP13B had significant inhibitory effect on AP-1-dependent gene expression, but DUSP13A did not. To our knowledge, DUSP13B is the first identified testis-specific phosphatase that inhibits stress-activated MAPKs. These data suggest an important role for DUSP13B in protection from external stress during spermatogenesis.

Nanopore sensing has attracted much attention as a rapid, simple, and label-free single-molecule detection technology. To apply nanopore sensing to extensive targets including polypeptides, nanopores are required to have a size and structure suitable for the target. We recently designed a de novo β-barrel peptide nanopore (SVG28) that constructs a stable and monodispersely sized nanopore. To develop the sizes and functionality of peptide nanopores, systematic exploration is required. Here we attempt to use a cell-free synthesis system that can readily express peptides using transcription and translation. Hydrophilic variants of SVG28 were designed and expressed by the PURE system. The peptides form a monodispersely sized nanopore, with a diameter 1.1 or 1.5 nm smaller than that of SVG28. Such cell-free synthesizable peptide nanopores have the potential to enable the systematic custom design of nanopores and comprehensive sequence screening of nanopore-forming peptides.

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