( ( ( ( ( Researchers ( now ( had ( ( a handle ) ( on ( ( the events ) ( required ( to ( ( switch ( ( the kinase ) ( of titin ) ) ) on ) ) ) ) ) ) ) ) ) , ) but ) ( they ( still ( ( did n't ) ( know ( what ( ( the protein ) ( did ( in ( its ( active mode ) ) ) ) ) ) ) ) ) ) ) . )
(ROOT (S (S (NP (NNS Researchers)) (ADVP (RB now)) (VP (VBD had) (NP (NP (DT a) (NN handle)) (PP (IN on) (NP (NP (DT the) (NNS events)) (VP (VBN required) (S (VP (TO to) (VP (VB switch) (NP (NP (DT the) (NN kinase)) (PP (IN of) (NP (NN titin)))) (PP (IN on))))))))))) (, ,) (CC but) (S (NP (PRP they)) (ADVP (RB still)) (VP (VBD did) (RB n't) (VP (VB know) (SBAR (WHNP (WP what)) (S (NP (DT the) (NN protein)) (VP (VBD did) (PP (IN in) (NP (PRP$ its) (JJ active) (NN mode))))))))) (. .)))
Researchers now had a handle on the events required to switch the kinase of titin on, but they still didn't know what the protein did in its active mode.
(ROOT (S (NP (DT The) (ADJP (JJS largest) (VBN known)) (NNS proteins)) (VP (VBP are) (ADJP (JJ titins))) (. .)))