NMR assignments and secondary structure distribution of emfourin, a novel proteinaceous protease inhibitor

Emfourin (M4in) from Serratia proteamaculans is a new proteinaceous inhibitor of protealysin-like proteases (PLPs), a subgroup of the well-known and widely represented metallopeptidase M4 family. Although the biological role of PLPs is debatable, data published indicate their involvement in pathogenesis, including bacterial invasion into eukaryotic cells, suppression of immune defense of some animals, and destruction of plant cell walls. Gene colocalization into a bicistronic operon observed for some PLPs and their inhibitors (as in the case of M4in) implies a mutually consistent functioning of both entities. The originality of the amino acid sequence of M4in suggests it belongs to a previously unknown protein family and this encourages structural studies. In this work, we report a near-complete assignment of ¹H, ¹³C, and ¹⁵N resonances of recombinant M4in and its structural-dynamic properties derived from the chemical shifts. According the NMR data analysis, the M4in molecule comprises 3-5 helical elements and 4-6 β-strands, at least two of which are apparently antiparallel, ascribing this obviously globular protein to the α + β structural class. Besides, two disordered regions also exist in the central loops between the regular secondary structural elements. The obtained data provide the basis for determining the high-resolution structure as well as functioning mechanism of M4in that can be used for development of new antibacterial therapeutic strategies.