Beschreibung:
<jats:p>Cyclophilins are folding helper enzymes and represent a family of the enzyme class of peptidyl‐prolyl <jats:italic>cis–trans</jats:italic> isomerases. Here, we report the molecular cloning and biochemical characterization of <jats:italic>San</jats:italic>Cyp18, an 18‐kDa cyclophilin from <jats:italic>Streptomyces antibioticus</jats:italic> ATCC11891 located in the cytoplasm and constitutively expressed during development. Amino acid sequence analysis revealed a much higher homology to cyclophilins from Gram negative bacteria than to known cyclophilins from <jats:italic>Streptomyces</jats:italic> or other Gram positive bacteria. <jats:italic>San</jats:italic>Cyp18 is inhibited weakly by CsA, with a <jats:italic>K</jats:italic>
<jats:sub>i</jats:sub> value of 21 μM, similar to cyclophilins from Gram negative bacteria. However, this value is more than 20‐fold higher than the <jats:italic>K</jats:italic>
<jats:sub>i</jats:sub> values reported for cyclophilins from other Gram positive bacteria, which makes <jats:italic>San</jats:italic>Cyp18 unique within this group. The presence of <jats:italic>San</jats:italic>Cyp18 in <jats:italic>Streptomyces</jats:italic> is likely due to horizontal gene transmission from Gram‐negative bacteria to <jats:italic>Streptomyces</jats:italic>.</jats:p>