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. 2009 Oct 7;97(7):2034-43.
doi: 10.1016/j.bpj.2009.07.034.

Unusual thermal disassembly of the SPFH domain oligomer from Pyrococcus horikoshii

Yohta Kuwahara  1 , Satoru Unzai, Takashi Nagata, Yoko Hiroaki, Hideshi Yokoyama, Ikuo Matsui, Takahisa Ikegami, Yoshinori Fujiyoshi, Hidekazu Hiroaki
Affiliations

Unusual thermal disassembly of the SPFH domain oligomer from Pyrococcus horikoshii

Yohta Kuwahara et al. Biophys J. .

Abstract

Stomatin, prohibitin, flotillin, and HflK/C (SPFH) domain proteins are membrane proteins that are widely conserved from bacteria to mammals. The molecular functions of these proteins have not been established. In mammals, the domain is often found in raft-associated proteins such as flotillin and podocin. We determined the structure of the SPFH domain of PH0470 derived from Pyrococcus horikoshii using NMR. The structure closely resembles that of the SPFH domain of the paralog PH1511, except for two C-terminal helices. The results show that the SPFH domain forms stable dimers, trimers, tetramers, and multimers, although it lacks the coiled-coil region for oligomerization, which is a highly conserved region in this protein family. The oligomers exhibited unusual thermodynamic behavior, as determined by circular dichroism, NMR, gel filtration, chemical cross-linking, and analytical ultracentrifugation. The oligomers were converted into monomers when they were heated once and then cooled. This transition was one-way and irreversible. We propose a mechanism of domain swapping for forming dimers as well as successive oligomers. The results of this study provide what to our knowledge are new insights into the common molecular function of the SPFH domain, which may act as a membrane skeleton through oligomerization by domain swapping.

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Figures

Figure 1
Figure 1
Sequence alignment and domain architecture of the SPFH domain. (A) Multiple sequence alignment domain-containing proteins. The secondary structure elements of PH0470SPFH are shown at the top of the diagram as open (α-helices), hatched (310-helix), and solid (β-strands) boxes. The residues corresponding to the subdomain latch are shown by an asterisk. Protein names and GenBank accession numbers are as follows: PH0470 (P. horikoshii; National Center for Biotechnology Information accession number NP_142449), PH1511 (P. horikoshii, NP_143371), YbbK (E. coli, YP_851665), Stomatin (human, NP_004090), Stomatin-like protein 3 (human, NP_660329), MEC-2 (C. elegans, AAA87552), Podocin (human, NP_055440), Flotillin 2 (human, NP_004466). (B) Domain arrangements and positions of the predicted coiled-coil region for SPFH domain-containing proteins. Open boxes are transmembrane helices, hatched boxes are the SPFH domains, and solid boxes show the coiled-coil region.
Figure 2
Figure 2
Oligomer formation of PH0470SPFH. (A) Gel-filtration profiles of PH0470SPFH. The upper panel shows the elution pattern without heat treatment; the lower panel shows the pattern with heat treatment. (B) Distribution of molar mass (c(M)) for PH0470SPFH. The c(s) distribution was converted to a molar mass distribution c(M). The upper panel shows the c(M) distribution without heat treatment; the lower panel shows the distribution with heat treatment. (C) Chemical cross-linking, PH0470SPFH (0.8 mg/mL) with glutaradehyde (0.05%) for 60 min at room temperature. Each sample was resolved using SDS-PAGE and stained with Coomassie brilliant blue. Numbers on the left indicate MW markers. The size of each oligomer state is shown to the right of the gel.
Figure 3
Figure 3
Solution structure of PH0470SPFH. (A) 1H-15N HSQC spectrum of PH0470SPFH. Numbers show residue assignments. (B) The best fit superposition of the 20 structures with the fewest structural violations. (C) Structural comparison of SPFH domain: left, PH1511SPFH; middle, PH0470SPFH; and right, FlotillinSPFH. The residues, which may destabilize the putative helix between β4 and α1 (Y106) in PH0470SPFH and the corresponding residue in PH1511SPFH (T103) is shown in blue.
Figure 4
Figure 4
Surface characteristics of PH0470SPFH. (A) Electrostatic surface potential diagrams with positive (blue) and negative (red) electrostatic potentials mapped onto a van der Waals surface diagram of the conserved surface patch. The color scale ranges between −20 kBT (red) and +20 kBT (blue), where kB is Boltzmann's constant and T is temperature. (B) Sequence conservation with variable (cyan) and conservative (purple) residues is mapped onto the surface. This figure was produced by ConSurf (34) and MOLMOL (38). A front view (left) and rear view (right) are shown. Ribbon diagram of PH0470SPFH in the same molecular orientations as in A and B.
Figure 5
Figure 5
NMR chemical shift differences between the backbone amide and 15N resonances of the PH0470SPFH monomer and those of the PH0470SPFH dimer. (A) 1H-15N HSQC spectrum of PH0470SPFH monomer and dimer. The monomer spectrum is shown in black; the dimer spectrum is shown in red. (B) NMR chemical shift differences between the backbone amide and 15N resonances of PH0470SPFH monomer and dimer. The chemical shift changes were calculated using the equation {(δN × 0.2)2 + δHN2}1/2, where δN and δHN are the chemical shift differences between the backbone nitrogen resonances and the amide proton resonances, respectively. (C) The surface residues indicated in light and dark green showed medium and large signal changes (δ > 0.05 and δ > 0.10, respectively) mapped on the surface of PH0470SPFH.
Figure 6
Figure 6
Domain swap oligomer model of PH0470SPFH. (A) PH0470SPFH monomer structure. Left: The α-helical region is shown in red, and β-sheet is shown in cyan. The region shown by an arrow corresponds to the hinge region. The region enclosed in the orange circle corresponds to the latch region. Right: Simplified model of PH0470SPFH monomer structure. Red and cyan boxes represent the α-helical and β-sheet subdomains, respectively. (B) PH0470SPFH dimer model structure by 3D-domain swapping (left) with simplified block diagram (right). (C) Simplified model of trimer, tetramer, and multimer formation. (D) Negatively stained electron micrograph of the PH0470SPFH multimer.
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