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The introduction of several mutations resulted in the generation of improved mutants of the green fluorescent protein (GFP). A strong green (GFPsg25) and blue (BFPsg50) fluorescent protein, gave 50-fold-100-fold brighter fluorescence compared to wild-type GFP and BFP (Tyr66His), respectively, upon expression in mammalian cells. GFPsg25 and BFPsg50 have different excitation and emission maxima. This allows their use as an efficient dual-color tagging system and their independent detection in living cells.

The crystal structure of an activation intermediate of human gastricsin has been determined at 2.4 A resolution. The human digestive enzyme gastricsin (pepsin C) is an aspartic proteinase that is synthesized as the inactive precursor (zymogen) progastricsin (pepsinogen C or hPGC). In the zymogen, a positively-charged N-terminal prosegment of 43 residues (Ala 1p-Leu 43p; the suffix 'p' refers to the prosegment) sterically prevents the approach of a substrate to the active site. Zymogen conversion occurs in an autocatalytic and stepwise fashion at low pH through the formation of intermediates. The structure of the non-covalent complex of a partially-cleaved peptide of the prosegment (Ala 1p-Phe 26p) with mature gastricsin (Ser 1-Ala 329) suggests an activation pathway that may be common to all gastric aspartic proteinases.

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