Structural Insights into a Side Chain Cross-Linking Biarylitide P450 from RiPP Biosynthesis

Peptide side chain
cross-linking is an important feature of many
natural products, with an increasing number of examples catalyzed
by cytochrome P450s being reported from ribosomal biosynthesis pathways
in addition to well-known examples from nonribosomal peptide antibiotics.
Despite the dramatic recent increase in the number of enzymes and
reactions catalyzed, substrate bound structures of such P450s have
proven elusive to date. Here, we report the structural characterization
of the biarylitide cross-linking enzyme P450Blt in complex
with its pentapeptide substrate MRYLH. This structure, in combination
with computational and biochemical experiments, shows the importance
of key I-helix residues in this P450 in coordinating to the histidine
residue of the substrate and further that this appears to be central
to the specificity of this enzyme for generating a C–N link
between the tyrosine and histidine residues in the MRYLH substrate.
The structure of the P450Blt-MRYLH complex provides the
first insight into how peptide substrates can be accommodated within
P450s and offers insights into how other examples of related P450s
can accept the varied substrates that have recently been identified
using bioinformatic methods.