/*
    <div id="proto_1" data-state="open">Div 1 - proto open</div>
    <div id="">Div 2</div>
    <div id="proto_3" data-state="closed">Div 3 - proto closed</div>
    <div id="proto_4" data-state="open">Div 4 - proto open</div>
*/

var $el = $('div[id^=proto_]').filter('div[data-state=open]').css('color','red');