The specific aims of this proposal are to obtain high-resolution structures of the cGMP- binding domains of cGMP-dependent protein kinase I and II (PKGs) and to use the structural information to design activators specific for PKGs. As key receptors for cGMP, PKG I and II mediate most effects of cGMP-elevating drugs such as nitric oxide-releasing agents for the treatment of many hypertensive diseases and phosphodiesterase inhibitors for the treatment of erectile dysfunction. While PKG I and II are therapeutic targets fo treating hypertensive diseases such as arterial and pulmonary hypertension, heart failure, erectile dysfunction and osteoporosis, developing specific activators has been difficult mainly due to a lack of available structural information. To obtain structural information needed for developing specific activators of PKG I and II, our group recently determined crystal structures of a fragment of the regulatory domains of human PKG I and II that specifically bind cGMP and activate catalytic activity. My long-term goals are to understand the activation mechanism of PKG mediated by cGMP and to develop specific activators of PKG that can be used for treating hypertensive diseases. To achieve these goals, my plans are to understand the role of the non-selective A-domain in activation of PKG I, to understand the cyclic nucleotide selectivity mechanism of PKG II, to screen known cGMP analogs for isoform specific binding and activation, and determine their co-crystal structures and use the resulting structural information for developing isoform specific activators of PKG I and II.