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Structural characterization of a novel monotreme‐specific protein with antimicrobial activity from the milk of the platypus
Author(s) -
Newman Janet,
Sharp Julie A.,
Enjapoori Ashwantha Kumar,
Bentley John,
Nicholas Kevin R.,
Adams Timothy E.,
Peat Thomas S.
Publication year - 2018
Publication title -
acta crystallographica section f
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.572
H-Index - 37
ISSN - 2053-230X
DOI - 10.1107/s2053230x17017708
Subject(s) - monotreme , platypus , biology , lactation , zoology , genetics , taxonomy (biology) , pregnancy , systematics
Monotreme lactation protein (MLP) is a recently identified protein with antimicrobial activity. It is present in the milk of monotremes and is unique to this lineage. To characterize MLP and to gain insight into the potential role of this protein in the evolution of lactation, the crystal structure of duck‐billed platypus ( Ornithorhynchus anatinus ) MLP was determined at 1.82 Å resolution. This is the first structure to be reported for this novel, mammalian antibacterial protein. MLP was expressed as a FLAG epitope‐tagged protein in mammalian cells and crystallized readily, with at least three space groups being observed ( P 1, C 2 and P 2 1 ). A 1.82 Å resolution native data set was collected from a crystal in space group P 1, with unit‐cell parameters a = 51.2, b = 59.7, c = 63.1 Å, α = 80.15, β = 82.98, γ = 89.27°. The structure was solved by SAD phasing using a protein crystal derivatized with mercury in space group C 2, with unit‐cell parameters a = 92.7, b = 73.2, c = 56.5 Å, β = 90.28°. MLP comprises a monomer of 12 helices and two short β‐strands, with much of the N‐terminus composed of loop regions. The crystal structure of MLP reveals no three‐dimensional similarity to any known structures and reveals a heretofore unseen fold, supporting the idea that monotremes may be a rich source for the identification of novel proteins. It is hypothesized that MLP in monotreme milk has evolved to specifically support the unusual lactation strategy of this lineage and may have played a central role in the evolution of these mammals.