The coxsackievirus 2B protein increases efflux of ions from the endoplasmic reticulum and Golgi, thereby inhibiting protein trafficking through the Golgi.
Coxsackievirus infection leads to a rapid reduction of the filling state of the endoplasmic reticulum (ER) and Golgi Ca2+ stores. The coxsackievirus 2B protein, a small membrane protein that localizes to the Golgi and to a lesser extent to the ER, has been proposed to play an important role in this effect by forming membrane-integral pores, thereby increasing the efflux of Ca2+ from the stores. Here, evidence is presented that supports this idea and that excludes the possibility that 2B reduces the uptake of Ca2+ into the stores. Measurement of intra-organelle-free Ca2+ in permeabilized cells revealed that the ability of 2B to reduce the Ca2+ filling state of the stores was preserved at steady ATP. Biochemical analysis in a cell-free system further showed that 2B had no adverse effect on the activity of the sarco/endoplasmic reticulum calcium ATPase, the Ca2+-ATPase that transports Ca2+ from the cytosol into the stores. To investigate whether 2B specifically affects Ca2+ homeostasis or other ion gradients, we measured the lumenal Golgi pH. Expression of 2B resulted in an increased Golgi pH, indicative for the efflux of H+ from the Golgi lumen. Together, these data support a model that 2B increases the efflux of ions from the ER and Golgi by forming membrane-integral pores. We have demonstrated that a major consequence of this activity is the inhibition of protein trafficking through the Golgi complex.
Department of Medical Microbiology, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands.
Arjan S
AS
de Jong
Henk-Jan
HJ
Visch
Fabrizio
F
de Mattia
Michiel M
MM
van Dommelen
Herman G
HG
Swarts
Tomas
T
Luyten
Geert
G
Callewaert
Willem J
WJ
Melchers
Peter H
PH
Willems
Frank J
FJ
van Kuppeveld
D000255:Adenosine Triphosphate / Q000737:chemistry; D000818:Animals; D001692:Biological Transport; D002118:Calcium / Q000378:metabolism; D002460:Cell Line; D002522:Chlorocebus aethiops; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D006056:Golgi Apparatus / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007477:Ions; D009154:Mutation; D012519:Sarcoplasmic Reticulum / Q000378:metabolism; D014764:Viral Proteins / Q000378:metabolism / Q000502:physiology*
D007477:Ions; D014764:Viral Proteins; C097017:coxsackie B3 virus protein 2B; D000255:Adenosine Triphosphate; D002118:Calcium