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This density does not look at all like O-glycosylation. 
Best regards,
Herman


________________________________

	From: CCP4 bulletin board [mailto:[log in to unmask]] On Behalf Of Savvas Savvides
	Sent: Wednesday, November 24, 2010 2:48 PM
	To: [log in to unmask]
	Subject: Re: [ccp4bb] Strange density on Serine oxygen.
	
	
	Hi Vinson 
	is O-glycosylation possible at all given the origin of the protein and the expression system used? 
	best 
	Savvas
	
	
	



	On 24 Nov 2010, at 14:42, Vinson LIANG wrote:


		
		Dear Savas and all,
		 
		Thank you very much for all your quick suggestions.
		 
		I have tried Tyr and it turns out to fit the density very well. I will have the protein sequenced again to see if it is wrong sequece or O-linked glycosylation.
		 
		I'll let you know if it turns out to be O-linked glycosylation.
		 
		All the best,
		 
		Vinson 
		
		
________________________________

		发件人： Savvas Savvides <[log in to unmask]>
		收件人： Vinson LIANG <[log in to unmask]>
		抄 送： [log in to unmask]
		发送日期： 2010/11/24 (周三) 9:27:31 下午
		主 题： Re: [ccp4bb] Strange density on Serine oxygen.
		
		Hi Vinson 
		Beyond the possibility for another type of residue as already suggested by Phil and Mark, there is also the possibility of O-linked glycosylation of the serine and threonine, if your protein undergoes such post-translational modification and it has been expressed via an expression system that processes the protein in that way.
		Ser/Thr tandems are well known targets for O-glycosylation (http://www.cbs.dtu.dk/databases/OGLYCBASE/).

		best regards
		Savvas

		
		----
		Savvas Savvides
		Unit for Structural Biology @ L-ProBE
		Ghent University
		K.L. Ledeganckstraat 35, 9000 Ghent, Belgium
		Ph. +32  (0)472 928 519 http://www.LProBE.ugent.be/xray.html



		On 24 Nov 2010, at 13:10, Vinson LIANG wrote:


			
			Dear all,
			 
			I'm refining a structure and find some strange triangle density on the oxygen of Ser and Thr at the C terminus. One picture of the strange density is attached here. Could anyone please give me some suggestions on what this could be?
			 
			The buffer used during purification is PBS, Tris and NaCl. And crystallization condition contains PEG3,350 and Mg(NO3)2.
			 
			Thank you all in advance for any suggestion.
			 
			Best,
			 
			Vinson Liang
			 
			 

			 <triangle_density.gif>