Type the accession number for human alpha amylase into the big center search window. Select the CDD database from the pull-down menu. Click on SUBMIT QUERY.
The results window should confirm that this sequence is for alpha amylase. Click on SEARCH FOR SIMILAR DOMAIN ARCHETECTURE.
At the CDART page (Conserved Domain Architecture Retrieval Tool), scroll down and select the alpha amylase catalytic domain (pfam000128).
Expand the "[+]Structure" menu, which is collapsed by default. Then click on SHOW STRUCTURE: