Figure 4.
Availability of four-letter PDB codes versus time: this figure depicts the annual count of available four-letter PDB codes. Current projections anticipate exhaustion of four-letter PDB codes by the end of 2027.
Official websites use .gov
A
.gov website belongs to an official
government organization in the United States.
Secure .gov websites use HTTPS
A lock (
) or https:// means you've safely
connected to the .gov website. Share sensitive
information only on official, secure websites.