I2B is a small cytosolic protein that participates in vacuole fusion.
Saccharomyces cerevisiae vacuole inheritance requires two low molecular weight activities, LMA1 and LMA2. LMA1 is a heterodimer of thioredoxin and protease B inhibitor 2 (I2B). Here we show that the second low molecular weight activity (LMA2) is monomeric I2B. Though LMA2/I2B was initially identified as a protease B inhibitor, this protease inhibitor activity is not related to its ability to promote vacuole fusion: (i) Low Mr protease B inhibitors cannot substitute for LMA1 or LMA 2, (ii) LMA1 and LMA2 promote the fusion of vacuoles from a strain that has no protease B, (iii) low concentrations of LMA2 that fully inhibit protease B do not promote vacuole fusion, and (iv) LMA1, in which I2B is complexed with thioredoxin, is far more active than LMA2/I2B in promoting vacuole fusion and far less active in inhibiting protease B. These studies establish a new function for I2B.
Slusarewicz
P
P
Department of Biochemistry, Dartmouth Medical School, Hanover, NH 03755-3844, USA.
Xu
Z
Z
Seefeld
K
K
Haas
A
A
Wickner
W T
WT
D002850:Chromatography, Gel; D003001:Cloning, Molecular; D003600:Cytosol / Q000502:physiology; D019281:Dimerization; D004926:Escherichia coli; D006023:Glycoproteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D007700:Kinetics; D008561:Membrane Fusion; D011480:Protease Inhibitors / Q000378:metabolism*; D011994:Recombinant Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000502:physiology*; D013879:Thioredoxins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D014617:Vacuoles / Q000502:physiology*
D006023:Glycoproteins; D011480:Protease Inhibitors; D011994:Recombinant Proteins; C018169:yeast proteinase B inhibitor; D013879:Thioredoxins