4.D.3.1.5 Cellulose synthase and transporter, BcsA, which functions with BcsB (periplasmic protein with an N-terminal TMS) and BcsC (an 18 β-stranded outer membrane porin). The x-ray structure of the BcsA-B complex has been determined at 3.5 Å resolution (Morgan et al. 2013). Cellulose is synthesized and secreted by the membrane-integrated cellulose synthase. Substrate- and product-bound structures of BcsA provided the basis for
substrate recognition and demonstrated the stepwise elongation of
cellulose. Structural snapshots showed that BcsA
translocates cellulose via a ratcheting mechanism involving a 'finger
helix' that contacts the polymer's terminal glucose. Cooperating with
BcsA's gating loop, the finger helix moves 'up' and 'down' in response
to substrate binding and polymer elongation, respectively, thereby
pushing the elongated polymer into BcsA's transmembrane channel. This
mechanism was validated by tethering BcsA's finger helix,
which inhibits polymer translocation but not elongation (Morgan et al. 2016).
|
Accession Number: | Q3J125 |
Protein Name: | Putative cellulose synthase |
Length: | 788 |
Molecular Weight: | 87963.00 |
Species: | Rhodobacter sphaeroides (strain ATCC 17023 / 2.4.1 / NCIB 8253 / DSM 158) [272943] |
Number of TMSs: | 8 |
Substrate |
(1->4)-beta-D-glucan |
---|
1: MTVRAKARSP LRVVPVLLFL LWVALLVPFG LLAAAPVAPS AQGLIALSAV VLVALLKPFA
61: DKMVPRFLLL SAASMLVMRY WFWRLFETLP PPALDASFLF ALLLFAVETF SISIFFLNGF
121: LSADPTDRPF PRPLQPEELP TVDILVPSYN EPADMLSVTL AAAKNMIYPA RLRTVVLCDD
181: GGTDQRCMSP DPELAQKAQE RRRELQQLCR ELGVVYSTRE RNEHAKAGNM SAALERLKGE
241: LVVVFDADHV PSRDFLARTV GYFVEDPDLF LVQTPHFFIN PDPIQRNLAL GDRCPPENEM
301: FYGKIHRGLD RWGGAFFCGS AAVLRRRALD EAGGFAGETI TEDAETALEI HSRGWKSLYI
361: DRAMIAGLQP ETFASFIQQR GRWATGMMQM LLLKNPLFRR GLGIAQRLCY LNSMSFWFFP
421: LVRMMFLVAP LIYLFFGIEI FVATFEEVLA YMPGYLAVSF LVQNALFARQ RWPLVSEVYE
481: VAQAPYLARA IVTTLLRPRS ARFAVTAKDE TLSENYISPI YRPLLFTFLL CLSGVLATLV
541: RWVAFPGDRS VLLVVGGWAV LNVLLVGFAL RAVAEKQQRR AAPRVQMEVP AEAQIPAFGN
601: RSLTATVLDA STSGVRLLVR LPGVGDPHPA LEAGGLIQFQ PKFPDAPQLE RMVRGRIRSA
661: RREGGTVMVG VIFEAGQPIA VRETVAYLIF GESAHWRTMR EATMRPIGLL HGMARILWMA
721: AASLPKTARD FMDEPARRRR RHEEPKEKQA HLLAFGTDFS TEPDWAGELL DPTAQVSARP
781: NTVAWGSN