EX1 hydrogen-deuterium exchange in an all-helical protein and its cyclized derivative at neutral pH

► The all-helical protein, DnaBN, exhibited EX1 type hydrogen exchange at pH 7.2. ► The protein was cyclized by joining the N- and C-termini through peptide linkers that were three, four, five or nine amino acids long. ► The rate of exchange for the slowly exchanging protons decreased for both the linear and cyclized proteins as linker length increased, correlating with predictions that the C-terminal helix of the protein would be extended by addition of these extra amino acids and stabilizing the protein.