Crystal Structure of a Secreted Insect Ferritin Reveals a Symmetrical Arrangement of Heavy and Light Chains
Abstract
Ferritins are iron storage proteins made of 24 subunits forming a hollow spherical shell. Vertebrate ferritins contain varying ratios of heavy (H) and light (L) chains; however, known ferritin structures include only one type of chain and have octahedral symmetry. Here, we report the 1.9 Å structure of a secreted insect ferritin from Trichoplusia ni, which reveals equal numbers of H and L chains arranged with tetrahedral symmetry. The H/L-chain interface includes complementary features responsible for ordered assembly of the subunits. The H chain contains a ferroxidase active site resembling that of vertebrate H chains with an endogenous, bound iron atom. The L chain lacks the residues that form a putative iron core nucleation site in vertebrate L chains. Instead, a possible nucleation site is observed at the L chain 3-fold pore. The structure also reveals inter- and intrasubunit disulfide bonds, mostly in the extended N-terminal regions unique to insect ferritins. The symmetrical arrangement of H and L chains and the disulfide crosslinks reflect adaptations of insect ferritin to its role as a secreted protein.
Additional Information
© 2005 Elsevier Ltd. Received 15 February 2005; received in revised form 23 March 2005; accepted 25 March 2005. We thank Peter Snow of the Caltech Protein Expression Center for supernatants of baculovirus-infected insect cells, the Caltech Protein/Peptide MicroAnalytical Laboratory for N-terminal protein sequencing, Matthew Walsh at IPFW for helpful mathematical discussions, Elizabeth Sprague for technical assistance, and members of the Bjorkman laboratory for critical reading of the manuscript. This work was supported by a career research award from the Burroughs-Wellcome Fund (to A.P.W.) and the Howard Hughes Medical Institute (to P.J.B.). A.E.H. was supported by the Whitehead Institute for Biomedical Research. Data Bank accession numbers: Atomic coordinates and structure factors have been deposited in the RCSB Protein Data Bank with accession code 1Z6O. The sequences of the T. ni H and L chain cDNAs have been deposited in GenBank with accession codes AY970291 (H chain) and AY970292 (L chain).Attached Files
Supplemental Material - mmc1.doc
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Additional details
- Eprint ID
- 75437
- DOI
- 10.1016/j.jmb.2005.03.074
- Resolver ID
- CaltechAUTHORS:20170327-143923217
- Burroughs-Wellcome Fund
- Howard Hughes Medical Institute (HHMI)
- Whitehead Institute for Biomedical Research
- Created
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2017-03-27Created from EPrint's datestamp field
- Updated
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2021-11-15Created from EPrint's last_modified field