What do you specifically want with PTEN tumor suppressor? If you want to check any mutation in this gene you should work with full length CDS. If you want to study its function you can try with only functional domain.

I am interested in studying its function. Thank  you.

 If you have only the functional domain, you may want to check whether this domain is responsible for binding or interacting with other proteins or DNA structure. And this can be assessed by a number of strategies such as yeast hybrid assays. I would like to suggest you to read this article in case you have not checked it yet. And also you may find important info about the structure and functions of this tumor suppressor in this article. Best of luck.