研究发现糖在细胞的生命周期充当重要角色(2)

On  the  other  hand,  cells  that  had  higher  than  normal  amounts  of  the  enzyme  that  removes  the  sugar  from  proteins  ended  up  with  nuclei  that  didn't  look  right  under  a  powerful  microscope.  Instead  of  being  disseminated  fairly  uniformly  through  the  entire  nucleus,  the  genetic  material  of  these  cells  was  bunched  up,  giving  the  contents  of  the  nucleus  a  "wrinkly"  appearance.

Exactly  what  is  going  wrong  is  still  unclear,  adds  Gerald  Hart,  Ph.D.,  professor  and  director  of  biological  chemistry.  He's  been  studying  O-GlcNAc  since  his  lab  discovered  it  attached  to  proteins  inside  cells  20  years  ago.  They  now  know  which  enzymes  put  the  sugar  onto  proteins  and  which  enzymes  take  it  off  --  and  knocking  out  or  blocking  these  enzymes  allowed  the  researchers  to  control  whether  proteins  were  sugar-laden  or  sugar-free.

"Normally,  the  enzyme  that  adds  the  sugar  to  proteins  is  enriched  at  the  hub  of  activity  during  cell  division,"  notes  Slawson.  "When  we  knock  it  out  or  block  it  with  a  chemical,  the  cell  cycle  lengthens  and  cell  division  doesn't  happen  properly.  Clearly  the  enzyme  is  there  for  a  reason."

But  understanding  what  the  sugar  itself  is  doing  and  how  its  presence  on  or  absence  from  proteins  affects  the  cell  depends  solely  on  what  protein  it's  being  attached  to  or  removed  from.

"Whether  it's  turning  something  on  or  off  depends  on  the  protein  to  which  the  sugar  is  attached,"  says  Hart.  "It's  harder  than  having  discovered  an  enzyme  that  does  just  one  thing.  To  figure  out  the  sugar's  effect,  we  have  to  look  at  what  it's  modifying,  and  the  extent  and  the  location  of  the  modification."

The  sugar  seems  to  modify  as  many  proteins  as  the  ubiquitous  phosphate  groups  widely  recognized  as  protein  controllers,  and  it  frequently  seems  to  compete  with  phosphate  groups  for  the  same  spots  on  proteins.  Hart  suggests  that  a  particular  balance  between  O-GlcNAc  and  phosphates  on  proteins  may  help  fine-tune  their  activities.   (责任编辑：泉水)

搜索

热门标签:

研究发现糖在细胞的生命周期充当重要角色(2)