cAPK (cAMP-dependent protein kinase) transfers the terminal phosphoryl group from ATP (adenosine-triphosphate) to the OH-side chain of serine or threonine residues of suitable substrate proteins.
This kind of phosphorylation is one of the key mechanism in the regulation of the cell.

First, we start taking a look at the X-ray structure of the catalytic subunit and examine the corresponding pdb file 1ATP.pdb

Questions:
From which organism does the sequence originate ?
Which organism was used for the expression of the protein ?
What is the reported maximum resolution ?
Which other (non-protein) molecules are present in the structure ?
Find the active center.

In this pdb file no link to a sequence data bank is given.
Find out the corresponding (primary) accession number in the UniProtKB data bank.

Try to imagine the consequences of the exchange of Asp166 against Ala. Will there be a significant structural change in the protein structure or not ?
Carry out this mutation using the sequnce in the FASTA format p05132.txt.

Use the modified sequence as input for the Swiss-Model Server
and click template identification to obtain suggestions for template structures. This may take several minutes... Select a template with high sequence identity and good resolution. Build Model will generate the homology model. Download your model in PDB format as well as the template structure. Superimpose both of them.
Are there crucial changes of the protein structure at all ?
Inspect the Model-Template Alignment. Which regions are predicted to be less well modelled (and why)? What do the GMQE and QMEAN scores mean?