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Results: 7

1.
Figure 1

Figure 1. From: Sugar recognition by CscB and LacY.

Chemical structures of sucrose, fructose, lactulose and β-galactopyranosides, where R represents different anomeric moieties (eg. in galactose R is H; in lactose R is glucose).

Junichi Sugihara, et al. Biochemistry. ;50(51):11009-11014.
2.
Figure 5

Figure 5. From: Sugar recognition by CscB and LacY.

Lactulose transport activity of CscB. Time courses of lactulose accumulation by E. coli T184 expressing CscB (●) or no permease (∘) were measured at 20 mM [3H]lactulose (0.1 mCi/mmol) as described in Materials and Methods.

Junichi Sugihara, et al. Biochemistry. ;50(51):11009-11014.
3.
Figure 3

Figure 3. From: Sugar recognition by CscB and LacY.

Effect of glucose on sucrose transport by CscB. Initial rates of [14C]sucrose accumulation by E. coli T184 cells expressing CscB were measured and fitted as described in Fig. 2B in the absence of glucose (●) or in the presence of 10 mM (△), 20 mM (▽) and 30 mM (□) glucose.

Junichi Sugihara, et al. Biochemistry. ;50(51):11009-11014.
4.
Figure 6

Figure 6. From: Sugar recognition by CscB and LacY.

Lactulose transport activity of LacY. (A) Time courses of lactulose accumulation by E. coli T184 expressing LacY (●) or no permease (∘) were measured at 0.4 mM [3H]lactulose (5 mCi/mmol) as described in Materials and Methods. (B) Concentration dependence of initial rates of lactulose accumulation measured as described in Materials and Methods. A hyperbolic fit is shown as a solid line with estimated kinetic parameters Km = 0.24 ± 0.02 mM and Vmax = 49 nmol/min·mg protein.

Junichi Sugihara, et al. Biochemistry. ;50(51):11009-11014.
5.
Figure 7

Figure 7. From: Sugar recognition by CscB and LacY.

Sucrose molecule modeled in the putative sugar-binding site of CscB. The sugar-binding site of CscB is viewed from the cytoplasmic side with a sucrose molecule docked according to the findings presented in this paper. The fructofuranosyl moiety is in close contact with amino acid residues essential for sugar binding (3), which are in the N-terminal 6-helix bundle and presented as green sticks. Residues important for H+ translocation are located in C-terminal 6-helix bundle and shown as cyan sticks. Transmembrane helices are numbered with Roman numerals. The CscB model was build by homology modeling using the x-ray structure of LacY (PDB ID 1PV7) as template (2). The sucrose molecule (coordinates from PDB ID 1IW0) is presented as yellow sticks. The figure was generated with Pymol 1.3.

Junichi Sugihara, et al. Biochemistry. ;50(51):11009-11014.
6.
Figure 2

Figure 2. From: Sugar recognition by CscB and LacY.

Transport activity of CscB. (A) Time courses of [14C]sucrose (0.5 mCi/mmol) accumulation by E. coli T184 expressing CscB (●), LacY (▲) or no permease (∘) were measured at 4 mM sucrose as described in Materials and Methods. (B) Concentration dependence of the initial rates of sucrose accumulation by E. coli T184 cells expressing CscB measured as described in Materials and Methods. Hyperbolic fit shown as a solid line with estimated kinetic parameters Km = 6.7 ± 1.3 mM, Vmax = 130 nmol/min·mg protein. (C) Time courses of 6 mM [14C]D-fructose (0.3 mCi/mmol) accumulation were measured and presented as in panel (A). (D) Kinetic analysis of fructose transport by CscB carried out as described in panel (B) with estimated kinetic parameters for fructose: Km = 36 ± 4 mM, Vmax = 60 nmol/min·mg protein.

Junichi Sugihara, et al. Biochemistry. ;50(51):11009-11014.
7.
Figure 4

Figure 4. From: Sugar recognition by CscB and LacY.

Effect of fructofuranosides on sucrose transport by CscB. (A) Testing of different sugars for their ability to inhibit transport of sucrose. Accumulation of [14C]sucrose (4 mM) by E. coli T184 expressing CscB was measured as described in Fig. 2A for 10 min without additions (100% activity) or in the presence of 10 mM unlabeled fructose, sucrose, turanose, lactulose, or palatinose. (B) Concentration dependence of fructose inhibition. Initial rates of [14C]sucrose transport (30 sec) were measured as in panel A at various concentrations of unlabeled fructose (10, 20 or 40 mM). Insert demonstrates competitive inhibition of [14C]sucrose transport by 20 mM fructose (▲) with estimated Ki of ~ 30 mM and unchanged Vmax = 160 nmol/min·mg protein. A Dixon plot exhibits a linear fit to the data (broken line) with estimated Ki of ~ 50 mM.

Junichi Sugihara, et al. Biochemistry. ;50(51):11009-11014.

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