Evolutionary novelty in gravity sensing through horizontal gene transfer and high-order protein assembly
Fig 1
P. blakesleeanus OCTIN crystals.
(A) The upper panel shows Phycomyces asexual fruiting body development tracked over the course of 10 hours. The stalk is a single-celled sporangiophore and the sphere at its tip contains nuclei that develop into asexual spores. The asterisk indicates the approximate region where protein crystals occur. The lower panel shows a close-up view of protein crystals within the sporangiophore central vacuole. (B) Three focal planes reveal the octahedral structure of a purified crystal. The bottom panel shows a cartoon of the crystal geometry. The lightest triangular face corresponds to the first panel. The darkest triangular face corresponds to the third panel. (C) The crystal-enriched fraction analyzed by SDS-PAGE. Two prominent proteins, p55 and p14 are indicated. The asterisk identifies a 46-kDa band whose peptides are mapped to the same region as p55 by mass spectrometry. (D) The cartoon depicts the full-length OCTIN sequence. Peptides identified from p14 and p55 are shown in blue and yellow, respectively. The N-termini of the mature proteins are indicated (arrowheads). The dashed line identifies the predicted region removed through proteolytic processing based on the molecular weight of p14. An asterisk marks the position of a stop-codon in the crystal-less mutant. (E) An organismal phylogeny showing the distribution of taxa where full-length OCTIN homologs are found. Names of these taxa are in colored or black labels. Gray colored groups do not contain OCTIN. OCTIN, octahedral crystal matrix protein.