Keyhole limpet hemocyanin (KLH): 9A cryoEM structure and molecular model of the didecamer reveal the interfaces and intricate topology of the 160 functional units
Journal: J Mol Biol / Year: 2009 Title: Keyhole limpet hemocyanin: 9-A CryoEM structure and molecular model of the KLH1 didecamer reveal the interfaces and intricate topology of the 160 functional units. Authors: Christos Gatsogiannis / Jürgen Markl / Abstract: Hemocyanins are blue copper-containing respiratory proteins in the hemolymph of many arthropods and molluscs. Molluscan hemocyanins are decamers, didecamers, or multidecamers of a 340- to 400-kDa ...Hemocyanins are blue copper-containing respiratory proteins in the hemolymph of many arthropods and molluscs. Molluscan hemocyanins are decamers, didecamers, or multidecamers of a 340- to 400-kDa polypeptide subunit containing seven or eight globular functional units (FUs; FU-a to FU-h), each with an oxygen-binding site. The decamers are short 35-nm hollow cylinders, with their lumen narrowed by a collar complex. Our recently published 9-A cryo-electron microscopy/crystal structure hybrid model of a 3.4-MDa cephalopod hemocyanin decamer [Nautilus pompilius hemocyanin (NpH)] revealed the pathway of the seven-FU subunit (340 kDa), 15 types of inter-FU interface, and an asymmetric collar consisting of five "arcs" (FU-g pairs). We now present a comparable hybrid model of an 8-MDa gastropod hemocyanin didecamer assembled from two asymmetric decamers [isoform keyhole limpet hemocyanin (KLH) 1 of the established immunogen KLH]. Compared to NpH, the KLH1 subunit (400 kDa) is C-terminally elongated by FU-h, which is further extended by a unique tail domain. We have found that the wall-and-arc structure of the KLH1 decamer is very similar to that of NpH. We have traced the subunit pathway and how it continues from KLH1-g to KLH1-h to form an annulus of five "slabs" (FU-h pairs) at one cylinder edge. The 15 types of inter-FU interface detected in NpH are also present in KLH1. Moreover, we have identified one arc/slab interface, two slab/slab interfaces, five slab/wall interfaces, and four decamer/decamer interfaces. The 27 interfaces are described on the basis of two subunit conformers, yielding an asymmetric homodimer. Six protrusions from the cryo-electron microscopy structure per subunit are associated with putative attachment sites for N-linked glycans, indicating a total of 120 sugar trees in KLH1. Also, putative binding sites for divalent cations have been detected. In conclusion, the present 9-A data on KLH1 confirm and substantially broaden our recent analysis of the smaller cephalopod hemocyanin and essentially solve the gastropod hemocyanin structure.
History
Deposition
Oct 6, 2008
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Header (metadata) release
Oct 7, 2008
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Map release
Nov 12, 2010
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Update
Jan 8, 2014
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Current status
Jan 8, 2014
Processing site: PDBe / Status: Released
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Structure visualization
Movie
Surface view with section colored by density value
Name: Keyhole Limpet Hemocyanin Isoform 1 (KLH1) / type: sample / ID: 1000 Oligomeric state: KLH1 is a didecamer of a 400 kDa subunit. Each subunit is composed by 8 paralogous O2 binding functional units Number unique components: 1
pH: 7.4 / Details: 50 mM Tris-Hcl, 150 mM NaCl, 5mM CaCl, 5mM MgCl2
Staining
Type: NEGATIVE / Details: cryoEM, no stain
Grid
Details: 400 mesh copper
Vitrification
Cryogen name: ETHANE / Chamber temperature: 86 K / Instrument: HOMEMADE PLUNGER Details: Vitrification instrument: Home made. Vitrification carried out in 25 percent oxygen atmosphere Method: Single side blotting and rapid plunging
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Electron microscopy
Microscope
FEI TECNAI 20
Temperature
Average: 86 K
Date
Jul 25, 2007
Image recording
Category: FILM / Film or detector model: KODAK SO-163 FILM / Digitization - Scanner: PRIMESCAN / Digitization - Sampling interval: 1.24 µm / Number real images: 98 / Bits/pixel: 8
Electron beam
Acceleration voltage: 200 kV / Electron source: FIELD EMISSION GUN
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