BetaCore, a designed water soluble four‐stranded antiparallel β‐sheet protein

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Abstract
BetaCore is a designed ∼50‐residue protein in which two BPTI‐derived core modules, CMIand CMII, are connected by a 22‐atom cross‐link. At low temperature and pH 3, homo‐ and heteronuclear NMR data report a dominant folded (′f') conformation with well‐dispersed chemical shifts,i, i+1 periodicity, numerous long‐range NOEs, and slowed amide hydrogen isotope exchange patterns that is a four‐stranded antiparallel β‐sheet with nonsymmetrical and specific association of CMIand CMII. BetaCore 'f' conformations undergo reversible, global, moderately cooperative, non‐two‐state thermal transitions to an equilibrium ensemble of unfolded 'u' conformations. There is a significant energy barrier between 'f' and 'u' conformations. This is the first designed four‐stranded antiparallel β‐sheet that folds in water.