Pull down assay showed that r p 55 protein interacted with r p 55 itself and various PSD proteins , such as PSD 95 , SAP 97 , GKAP , CASK , GRIP , neuroligin , cadherin , tubulin , actin , alpha internexin , neurofilament L and Ca ( 2+ ) / calmodulin dependent protein kinase 2 , through its PDZ , SH 3 , HOOK or GK domains . ^^^