This web page was produced as an assignment for an undergraduate course at Davidson College
FhuA, as mentioned on the introductory webpage, is a monomeric protein found in the outer membrane of Escherichia coli. It acts as an energy dependent protein channel whose primary function is to transport ferrichrome-iron across the outer membrane of E. coli. It derives energy from a Ton based protein complex (consisting of TonB, ExbB, and ExbD) located in the cytoplasmic membrane of E. coli (Ferguson et al 1998). In addition to acting as a ferrichrome-iron receptor, FhuA also acts as a primary receptor for the antibiotic albomycin, four bacteriphages (T1, T5, UC-1, and f80), the peptide antibiotic microcin 25, and the bacterial toxin colicin M (Braun 1998). Since FhuA is a bacterial outer membrane protein, and only prokaryotic organisms have a double outer membrane, it does not have any true orthologs in any eukaryotic organisms; however, there is one predicted ortholog to the FhuA protein found in the mitochondria of the common mosquito.
The FhuA protein found in E. coli consists of 714 residues (Figure 1 ). There are many other prokaryotic organisms that produce this exact amino sequence, and, subsequently, express the same FhuA protein in their outer membranes. There are also some other prokaryotes that conserve most of this sequence, but not all of it. Therefore, these organisms express phenotypes that are slightly different than those that have the FhuA protein sequence completely conserved. The primary organism used to study the FhuA protein is E. coli, and little research has been conducted on this protein in other prokaryotes; thus, much of what is known about the function of FhuA in organisms other than E. coli is assumed based upon what is known about its function in E. coli.
1 marsktaqpk hslrkiavvv atavsgmsvy aqaavepked titvtaapap qesawgpaat
61 iaarqsatgt ktdtpiqkvp qsisvvtaee malhqpksvk ealsytpgvs vgtrgasnty
121 dhliirgfaa egqsqnnyln glklqgnfyn davidpymle raeimrgpvs vlygksspgg
181 llnmvskrpt teplkevqfk agtdslfqtg fdfsdslddd gvysyrltgl arsanaqqkg
241 seeqryaiap aftwrpddkt nftflsyfqn epetgyygwl pkegtveplp ngkrlptdfn
301 egaknntysr nekmvgysfd hefndtftvr qnlrfaenkt sqnsvygygv csdpanaysk
361 qcaalapadk ghylarkyvv ddeklqnfsv dtqlqskfat gdidhtlltg vdfmrmrndi
421 nawfgyddsv pllnlynpvn tdfdfnakdp ansgpyriln kqkqtgvyvq dqaqwdkvlv
481 tlggrydwad qeslnrvagt tdkrddkqft wrggvnylfd ngvtpyfsys esfepssqvg
541 kdgnifapsk gkqyevgvky vpedrpivvt gavynltktn nlmadpegsf fsveggeira
601 rgveieakaa lsasvnvvgs ytytdaeytt dttykgntpa qvpkhmaslw adytffdgpl
661 sgltlgtggr ytgssygdpa nsfkvgsytv vdalvrydla rvgmagsnva lhvnnlfdre
721 yvascfntyg cfwgaerqvv atatfrf
Actinobacillus pleyropneymoniae:
The bacteria A. pleyropneymoniae, a bacteria known for causing a highly infectious disease in pigs, expresses a protein nearly identical to that found in E. coli. This ortholog has been studied extensively, and has been proven to act as a ferrichrome-iron receptor for the A. pleyropneymoniae bacteria, just as FhuA acts in E. coli (Mikael et al). Although it is known to act as a ferrichrome-iron uptake protein, it is not known if this particular protein shares any other similarities with FhuA from E. coli, such as acting as a receptor for the antibiotic albomycin, the bacteriphages T1, T5, UC-1, and f80, the peptide antibiotic microcin 25, and the bacterial toxin colicin M (Braun 1998).
1 mkktffystv asavalaisp aiaqetavld evsvvssgsm ykmgevpvhq aksavaisre
61 dldkqdvkka deigryqagf anqvfgndtn tnwfrvrgee vsqavdglpt fsygfftpyv
121 ktfgleavev tkgadsmtfg aansggliny vtkrahrdqi grgefktnfg snnlygfgad
181 ytgkitdden vryrvvasln htdgewkdtd nktvyiapsl ewdisdrtrl siltsyqkds
241 gtpssnfypq egtlralpdg syysrnvnfg dpvnnheenk qysigyelsh dfgnglrans
301 syryshvenn hrggyiypsa yaadwsavap sangynvsgq tvfnqgkais hstdnriswd
361 fkndwlkntv vvgtdyrhnk vdaqyslyal gytanlrdyr atwnqtgtpv gtdthiksrq
421 lgfylqnqar iadkyllgfg irhdrarqne ytsdqtvknn htsysgslmy egayglnpyf
481 sysesfrlpv glsgnqslyd pnitrqyelg vkylptwldg vitlagfrak dtgalvnngt
541 gatissadpi yrkgfelqtd vnltenwnat laytytkaes eaatgektrq sliptntlaa
601 rtaysftdsv lngltvgagv rylghsvtsk gslyshvrlp satvvdlmar yninqnwlaq
661 lnvdnvgnrk yvaacdyycy ygaerkvnat vsykf
Figure 2. Sequence of the A. pleyropneymoniae ortholog to FhuA. This sequence has been proven in studies to form a protein extremely similar in function to that of the FhuA protein found in E. coli . Sequence provided by NCBI.
Xanthomonas oryzae:
The bacteria Xanthomonas oryzae expresses a protein very similar to the FhuA protein found in E. coli. Extensive research has not yet been performed on this protein yet, however, and thus, the exact function of the protein is not known. Because of its striking similarity to the FhuA protein, it is thought to be a Ton B dependent receptor, but as of yet this is merely hypothetical (Lee et al).
1 mvgtrsmrtt asvsvdeiqv qvpgmapqql laslpgvkht rrllddrltm efgakgldvk
61 rdyngianld dftvgmrrav tiknsdwfqp qvgasfqlae gvqvfandae nfssaprltl
121 tsgafhpdia peesthidig iraestqwsg yiaackidde nriialtdpa llvvaptvya
181 nvgdvqtyga evsgmwkpap gwrlgtsltw nnseipgqlf rpgqrqpgtg erqrgagcae
241 gdvqrqrrlg rraflrqfrr qihrqalrrh vqdrpggchl hrqrqrrvsg rgqwvacrws
301 aavvglhpvr qarydrcgvs qrklrlvpvd rtapavrqsg rhilrcsrgr qgcrphafvh
361 dmrgkcvdar qshgsddaaa iadahrydrr rrddvsgdeq pghggriqfq rpaatgwrpq
421 ggvgldsrcr agrherrlrv aqgrlpraaa
Figure 3. Sequence of a hypothetical X. oryzae ortholog to FhuA. Because the sequence of this protein was just recently determined, extensive research on this particular gene sequence has yet to be performed, and it is not yet known for sure if this gene does in fact code for a FhuA ortholog; however, it is suspected that it does. Sequence provided by NCBI.
Shigella flexneri 2a Strain 301
The bacteria Shigella flexneri, which is known to cause severe dysentery in humans, contains an amino sequence that is completely identical to the amino sequence that forms the FhuA protein in E. coli. Both S. flexneri and E. coli cause severe dysentery in humans, and they may be closely related, evolutionarily speaking. This hypothesis is supported by the similarity between these two proteins. In addition to acting as a ferrichrome-iron uptake protein in S. flexneri, this FhuA ortholog also acts as a receptor for the antibiotic albomycin, the bacteriphages T1, T5, UC-1, and f80, the peptide antibiotic microcin 25, and the bacterial toxin colicin M (Jin et al).
1 marsktaqpk hslrkiavvv atavsgmsvy aqaavepked titvtaapap qesawgpaat
61 iaarqsatgt ktdtpiqkvp qsisvvtaee malhqpksvk ealsytpgvs vgtrgasnty
121 dhliirgfaa egqsqnnyln glklqgnfyn davidpymle raeimrgpvs vlygksspgg
181 llnmvskrpt teplkevqfk agtdslfqtg fdfsdalddd gvysyrltgl arsanaqqkg
241 seeqryaiap aftwrpddkt nftflsyfqn epetgyygwl pkegtveplp ngkrlptdfn
301 egaknntysr nekmvgysfd hefndtftvr qnlrfaenkt sqnsvygygv csdpanaysk
361 qcaalapadk ghylarkyvv ddeklqnfsv dtqlqskfat gdidhtlltg vdfmrmrndi
421 nawfgyddsv plfnlynpvn pdfdfnakdp ansgpyriln kqkqtgvyvq dqaqwdkvlv
481 tlggrydwad qeslnrvagt tdkrddkqft wrggvnylfd ngvtpyfsys esfepssqvg
541 kdgnifapsk gkqyevgvky vpedrpivvt gavynltktn nlmadpegsf fsveggeira
601 rgveieakaa lsasvnvvgs ytytdaeytt dttykgntpa qvpkhmaslw adytffdgpl
661 sgltlgtggr ytgssygdpa nsfkvgsytv vdalvrydla rvgmagsnva lhvnnlfdre
721 yvascfntyg cfwgaerqvv atatfrf
Figure 4. Sequence of the S. flexneri ortholog to FhuA. This is the sequence to the FhuA ortholog found in S. flexneri. It is completely identical to that found in E. coli. Sequence provided by NCBI .
As mentioned perviously, there are no known true orthologs for the FhuA protein in any eukaryotic species. However, there is one hypothetical ortholog present in the mitochondria of the common mosquito.
Anopheles gambiae
The only FhuA ortholog even hypothesized to exist in a eukaryote as of yet is found in the mitochondria of Anopheles gambiae, or the common mosquito. Because FhuA is an outer membrane protein, it makes since that the eukaryotic ortholog would be located in the mitochondria of A. gambiae. Mitochondria are believed to have evolved from prokaryotic cells; thus, they have a dual layered membrane. Since it is only hypothetical that this protein is an ortholog of FhuA, it is not known if this protein actually maintains any of the functions of FhuA.
1 lvaatisall agpvqaaate rptqtradet ltvlgetyrn tatktrldpl etpqaisvve
61 gdtleqrgvs svsealryvp gvntelrgga vnrldlfnir gfdnyqnfyd glllqyndwn
121 lqpqidpvai eqlevfkgpt svlygsmppg gmvnliakrp qresrhsvsv asgtgtlkel
181 tldstgalne qfayrlvgla rqkegqavts eeeryvlaps ldwqlsdrtl lnlnlyyqkd
241 pqagiyttvp asgsvksnpl gqlgsdtflg denwnhysre vtllgyklsh dfnanwqllq
301 narymdasan qqntynaala adhrtlarna yltdeesrgf vidnqlagkv qtgkaqhnll
361 lgvdyqylda rilyrdtldy sapaidifnp nhqqivpadl afnyqdnrti rqyqsglylq
421 dqvrldrlva iggarydryr mdtdsrtlyq gaasnslaqi dqdnlslrlg alydldhgls
481 pyvsyaesfe pvagadkqgq afkpatgrqw egglkflsed vsktatisaf hitkenalvt
541 dpdnvygpkl qtgemvskgv elegrldlts rwdlalsytr qemeitrdtt slqgktpvwv
601 qkqmaslwsn ylpagplaga rlgaglryvg eaqldaantd tvpdyllmdm sasydlaqls
661 qrlqgvevsl sasnlfnkty yscydqnncw fgaersvear lkyvf
Figure 5. Sequence of the A. gambiae hypothetical ortholog to FhuA. This is the sequence to the hypothetical protein in the A. gambiae, or the mosquito, that is supposedly found in the mitochondria of the organism. Sequence provided by NCBI.
Braun V. 1998. Pumping Iron Through Cell Membranes. Science . 282: 2202-2203.
Ferguson AD, Hofmann E, Coulton JW, Diederichs K, Welte, Wolfram. 1998. Siderophore-Mediated Iron Transport: Crystal Structure of FhuA with Bound Lipopolysaccharide. Science . 282: 2215-2220.
Jin Q, Yuan Z, Xu J, Wang Y, Shen Y, Lu W, Wang J, Liu H, Yang J, Yang F, Zhang X, Zhang J, Yang G, Wu H, Qu D, Dong J, Sun L, Xue Y, Zhao A, Gao Y, Zhu J, Kan B, Ding K, Chen S, Cheng H, Yao Z, He B, Chen R, Ma D, Qiang B, Wen Y,Hou Y, Yu J. 2002. Genome sequence of Shigella flexneri 2a: insights into pathogenicity through comparison with genomes of Escherichia coli K12 and O157. Nucleic Acids Res. 30: 4432-4441.
Lee BM, Park YJ, Park DS, Kang HW, Kim JG, Song ES, Park IC, Yoon UH, Hahn JH, Koo BS, Lee GB, Kim H, Park HS, Yoon KO, Kim JH, Jung CH, Koh NH, Seo JS, Go SJ. 2005. The genome sequence of Xanthomonas oryzae, the bacterial blight pathogen of rice. Nucleic Acids Res. 33: 577-586.
Locher KP, Rees B, Koebnik R, Mitschler A, Moulinier L, Rosenbusch JP, Moras D. 1998. Transmembrane Signaling across the Ligand-Gated FhuA Receptor: Crystal Structures of Free and Ferrichrome-Bound States Reveal Allosteric Changes. Cell. 95: 771-778.
Mikael LG, Srikumar R, Coulton JW, Jacques M. 2003. fhuA of Actinobacillus pleuropneymoniae Encodes a Ferrichrome Recptor but Is Not Regulated by Iron. Infection and Immunity. 71: 2911-2915.
NCBI Sequence Viewer: Entrez Protein. <http://www.ncbi.nlm.nih.gov:80/entrez/query.fcgi?cmd=Retrieve&db=Protein&list_uids=55247232&dopt=GenPept> . Accessed 2005 Mar 07.