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Journal of Bacteriology, December 2005, p. 8137-8148, Vol. 187, No. 23
0021-9193/05/$08.00+0     doi:10.1128/JB.187.23.8137-8148.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Homodimeric Hexaprenyl Pyrophosphate Synthase from the Thermoacidophilic Crenarchaeon Sulfolobus solfataricus Displays Asymmetric Subunit Structures{dagger}

Han-Yu Sun,1,2 Tzu-Ping Ko,2 Chih-Jung Kuo,2 Rey-Ting Guo,1,4 Chia-Cheng Chou,2,3 Po-Huang Liang,1,2,4 and Andrew H.-J. Wang1,2,3,4*

Institute of Biochemical Sciences, National Taiwan University, Taipei 106,1 Institute of Biological Chemistry,2 Core Facility for Protein X-Ray Crystallography,3 Taiwan International Graduate Program, Academia Sinica, Taipei 115, Taiwan4

Received 20 June 2005/ Accepted 26 August 2005

Hexaprenyl pyrophosphate synthase (HexPPs) from Sulfolobus solfataricus catalyzes the synthesis of trans-C30-hexaprenyl pyrophosphate (HexPP) by reacting two isopentenyl pyrophosphate molecules with one geranylgeranyl pyrophosphate. The crystal structure of the homodimeric C30-HexPPs resembles those of other trans-prenyltransferases, including farnesyl pyrophosphate synthase (FPPs) and octaprenyl pyrophosphate synthase (OPPs). In both subunits, 10 core helices are arranged about a central active site cavity. Leu164 in the middle of the cavity controls the product chain length. Two protein conformers are observed in the S. solfataricus HexPPs structure, and the major difference between them occurs in the flexible region of residues 84 to 100. Several helices ({alpha}I, {alpha}J, {alpha}K, and part of {alpha}H) and the associated loops have high-temperature factors in one monomer, which may be related to the domain motion that controls the entrance to the active site. Different side chain conformations of Trp136 in two HexPPs subunits result in weaker hydrophobic interactions at the dimer interface, in contrast to the symmetric {pi}-{pi} stacking interactions of aromatic side chains found in FPPs and OPPs. Finally, the three-conformer switched model may explain the catalytic process for HexPPs.

* Corresponding author. Mailing address: Institute of Biological Chemistry, Academia Sinica, 128 Academia Road, Taipei 115, Taiwan. Phone: 886-2-2788-1981. Fax: 886-2-2788-2043. E-mail: ahjwang{at}gate.sinica.edu.tw.

{dagger} Supplemental material for this article may be found at http://jb.asm.org/.

Journal of Bacteriology, December 2005, p. 8137-8148, Vol. 187, No. 23
0021-9193/05/$08.00+0     doi:10.1128/JB.187.23.8137-8148.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.



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