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Human atlastin GTPases mediate differentiated fusion of endoplasmic reticulum membranes.

Hu X, Wu F, Sun S, Yu W, Hu J - Protein Cell (2015)

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Affiliation: Tianjin Key Laboratory of Protein Sciences, Department of Genetics and Cell Biology, College of Life Sciences, Nankai University, Tianjin, 300071, China.

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A class of membrane-bound dynamin-like GTPases called atlastins (ATLs) has been identified as mediating ER fusion (Hu et al., ; Orso et al., )... A similar class of dynamin-like GTPases has been identified in species lacking ATL, including Sey1p from Saccharomyces cerevisiae and Root Hair Defective 3 (RHD3) from Arabidopsis thaliana (Hu et al., ; Zhang and Hu, )... In mammals, ATL1 is predominantly localized to the central nervous system, whereas ATL2 and ATL3 are expressed in peripheral tissues (Rismanchi et al., )... Consistently, almost all HSP-causing mutations are found in ATL1 (Salinas et al., )... Yeast cells lacking Sey1p and one of the two proteins that shape the ER tubules (Yop1p or Rtn1p) exhibited abnormal cortical ER morphology; in particular, the tubular ER network largely disappeared and many areas of the cortex were void of ER, indicating a lack of ER fusion (Hu et al., )... CytATL2 exhibited similar GTP-induced dimerization as ATL1 (Fig.  2B), but little dimer was seen when ATL3 was tested at the same concentrations (Fig.  2C)... Finally, we compared the GTPase activities of purified cytATLs... The primary structures of these dynamin-like GTPases are highly conserved, with more than 60% sequence identity (Rismanchi et al., )... Some tissues, such as skeletal muscle, are enriched with ATL2, and others, such as the lung, contain more ATL3 (Rismanchi et al., )... The tissue distribution explains why almost all HSP-causing mutations are found in ATL1, given that HSP is a degenerative neuron disease... Notably, low levels of ATL3 are also found in brain tissue, which is consistent with a recent description of a rare case in which ATL3 mutation caused hereditary sensory neuropathy (Kornak et al., )... Another dynamin-like GTPase family in mammals, called mitofusin (MFN), also mediates homotypic membrane fusion (Hoppins et al., ), in this case in outer mitochondrial membranes, and has the same molecular architect and membrane topology as ATLs... Xiaoyu Hu, Fuyun Wu, Sha Sun, Wenying Yu, and Junjie Hu declare that they have no conflict of interest... This article does not contain any studies with human or animal subjects performed by the any of the authors.

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Biochemical comparison of cytATLs. Nucleotide-dependent dimerization of (A) cytATL1, (B) cytATL2, and (C) cytATL3 (12 μmol/L shown in blue, 24 μmol/L shown in red) were determined by analytical ultracentrifugation in the presence of GMP-PNP. The estimated molecular masses are given above the peaks (in kDa). (D) The GTPase activities of the N-terminal cytosolic domains of wt ATL1, ATL2, and ATL3 (0.2 μmol/L, 1 μmol/L, and 2.5 μmol/L) were measured by phosphate release at saturating concentrations of GTP (0.5 mmol/L). All graphs are representative of three repetitions
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Fig2: Biochemical comparison of cytATLs. Nucleotide-dependent dimerization of (A) cytATL1, (B) cytATL2, and (C) cytATL3 (12 μmol/L shown in blue, 24 μmol/L shown in red) were determined by analytical ultracentrifugation in the presence of GMP-PNP. The estimated molecular masses are given above the peaks (in kDa). (D) The GTPase activities of the N-terminal cytosolic domains of wt ATL1, ATL2, and ATL3 (0.2 μmol/L, 1 μmol/L, and 2.5 μmol/L) were measured by phosphate release at saturating concentrations of GTP (0.5 mmol/L). All graphs are representative of three repetitions

Mentions: Previous studies have shown that ATL-mediated fusion is initiated by GTP-dependent dimerization between ATL molecules in apposing membranes, and the reaction proceeds when GTP hydrolysis drives conformational changes in ATL. To test whether the varied fusion abilities of the three ATLs are caused by different dimerization tendencies of ATLs upon GTP binding, we compared the dimerization state of purified cytATLs using analytic ultra-centrifugation (AUC). At low concentrations (12 μmol/L), cytATL1 formed some dimer in the presence of GMP-PNP, a non-hydrolyzable analog of GTP (Fig. 2A). The proportion of dimer was increased in the presence of a higher concentration of cytATL1 (24 μmol/L, Fig. 2A). Previously, cytATL1 was shown to behave as a dimer when an even higher protein concentration (50 μmol/L) was used in AUC (Bian et al., 2011). CytATL2 exhibited similar GTP-induced dimerization as ATL1 (Fig. 2B), but little dimer was seen when ATL3 was tested at the same concentrations (Fig. 2C).Figure 2


Human atlastin GTPases mediate differentiated fusion of endoplasmic reticulum membranes.

Hu X, Wu F, Sun S, Yu W, Hu J - Protein Cell (2015)

Biochemical comparison of cytATLs. Nucleotide-dependent dimerization of (A) cytATL1, (B) cytATL2, and (C) cytATL3 (12 μmol/L shown in blue, 24 μmol/L shown in red) were determined by analytical ultracentrifugation in the presence of GMP-PNP. The estimated molecular masses are given above the peaks (in kDa). (D) The GTPase activities of the N-terminal cytosolic domains of wt ATL1, ATL2, and ATL3 (0.2 μmol/L, 1 μmol/L, and 2.5 μmol/L) were measured by phosphate release at saturating concentrations of GTP (0.5 mmol/L). All graphs are representative of three repetitions
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Fig2: Biochemical comparison of cytATLs. Nucleotide-dependent dimerization of (A) cytATL1, (B) cytATL2, and (C) cytATL3 (12 μmol/L shown in blue, 24 μmol/L shown in red) were determined by analytical ultracentrifugation in the presence of GMP-PNP. The estimated molecular masses are given above the peaks (in kDa). (D) The GTPase activities of the N-terminal cytosolic domains of wt ATL1, ATL2, and ATL3 (0.2 μmol/L, 1 μmol/L, and 2.5 μmol/L) were measured by phosphate release at saturating concentrations of GTP (0.5 mmol/L). All graphs are representative of three repetitions
Mentions: Previous studies have shown that ATL-mediated fusion is initiated by GTP-dependent dimerization between ATL molecules in apposing membranes, and the reaction proceeds when GTP hydrolysis drives conformational changes in ATL. To test whether the varied fusion abilities of the three ATLs are caused by different dimerization tendencies of ATLs upon GTP binding, we compared the dimerization state of purified cytATLs using analytic ultra-centrifugation (AUC). At low concentrations (12 μmol/L), cytATL1 formed some dimer in the presence of GMP-PNP, a non-hydrolyzable analog of GTP (Fig. 2A). The proportion of dimer was increased in the presence of a higher concentration of cytATL1 (24 μmol/L, Fig. 2A). Previously, cytATL1 was shown to behave as a dimer when an even higher protein concentration (50 μmol/L) was used in AUC (Bian et al., 2011). CytATL2 exhibited similar GTP-induced dimerization as ATL1 (Fig. 2B), but little dimer was seen when ATL3 was tested at the same concentrations (Fig. 2C).Figure 2

View Article: PubMed Central - PubMed

Affiliation: Tianjin Key Laboratory of Protein Sciences, Department of Genetics and Cell Biology, College of Life Sciences, Nankai University, Tianjin, 300071, China.

AUTOMATICALLY GENERATED EXCERPT
Please rate it.

A class of membrane-bound dynamin-like GTPases called atlastins (ATLs) has been identified as mediating ER fusion (Hu et al., ; Orso et al., )... A similar class of dynamin-like GTPases has been identified in species lacking ATL, including Sey1p from Saccharomyces cerevisiae and Root Hair Defective 3 (RHD3) from Arabidopsis thaliana (Hu et al., ; Zhang and Hu, )... In mammals, ATL1 is predominantly localized to the central nervous system, whereas ATL2 and ATL3 are expressed in peripheral tissues (Rismanchi et al., )... Consistently, almost all HSP-causing mutations are found in ATL1 (Salinas et al., )... Yeast cells lacking Sey1p and one of the two proteins that shape the ER tubules (Yop1p or Rtn1p) exhibited abnormal cortical ER morphology; in particular, the tubular ER network largely disappeared and many areas of the cortex were void of ER, indicating a lack of ER fusion (Hu et al., )... CytATL2 exhibited similar GTP-induced dimerization as ATL1 (Fig.  2B), but little dimer was seen when ATL3 was tested at the same concentrations (Fig.  2C)... Finally, we compared the GTPase activities of purified cytATLs... The primary structures of these dynamin-like GTPases are highly conserved, with more than 60% sequence identity (Rismanchi et al., )... Some tissues, such as skeletal muscle, are enriched with ATL2, and others, such as the lung, contain more ATL3 (Rismanchi et al., )... The tissue distribution explains why almost all HSP-causing mutations are found in ATL1, given that HSP is a degenerative neuron disease... Notably, low levels of ATL3 are also found in brain tissue, which is consistent with a recent description of a rare case in which ATL3 mutation caused hereditary sensory neuropathy (Kornak et al., )... Another dynamin-like GTPase family in mammals, called mitofusin (MFN), also mediates homotypic membrane fusion (Hoppins et al., ), in this case in outer mitochondrial membranes, and has the same molecular architect and membrane topology as ATLs... Xiaoyu Hu, Fuyun Wu, Sha Sun, Wenying Yu, and Junjie Hu declare that they have no conflict of interest... This article does not contain any studies with human or animal subjects performed by the any of the authors.

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