The alpha-amylase precursor from the bacterium Pseudoalteromonas haloplanktis possesses a propeptide at the C-terminus possibly responsible for outer membrane translocation. Unlike the predicted beta-barrel of autotransporters, this C-terminal propeptide displays a noticeable alpha-helix content. It is connected to the enzyme by a disordered linker and has no significant interaction with the catalytic domain. The microcalorimetric pattern of the precursor also demonstrates that the stability of protein domains may evolve differently.
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