how can i sort users pointing one of the column in table grid custom field in alphabetical order

[Sai Dinesh]

col.iresponsible=Responsible
col.iresponsible.type=userlist
col.iresponsible.required=true
col.iresponsible.autocomplete=false
col.iresponsible.width=400
col.iresponsible.allow.groups = jira-software-users

From the above code, it is displaying all the users in that user group but it is not getting displayed in alphabatical, order.