You are presented with a paragraph from a COVID-19 literature. Classify the topics of this piece of text by choosing from the following categories:

- Epidemic Forecasting: The content relates to predictions about the spread of COVID-19.
- Treatment: The paragraph discusses therapeutic methods or medication for COVID-19.
- Prevention: The content covers measures to prevent the spread of COVID-19.
- Mechanism: The paragraph explains the biological mechanisms of the virus.
- Case Report: The content is a report of a COVID-19 case.
- Transmission: The paragraph discusses how COVID-19 is transmitted.
- Diagnosis: The content is about diagnosing COVID-19 in individuals.

Your classification should be provided as an element within a JSON array. The array should be formatted with topics enclosed in double quotes and separated by commas, following the JSON format, for example: ["Topic1", "Topic2", ...]. Include all applicable topics within the array. Your output should be a valid JSON array, and no additional text should be included in your response.

Article:

The beta-link is a composite protein motif consisting of a G1beta beta-bulge and a type II beta-turn, and is generally found at the end of two adjacent strands of antiparallel beta-sheet. The 1,2-positions of the beta-bulge are also the 3,4-positions of the beta-turn, with the result that the N-terminal portion of the polypeptide chain is orientated at right angles to the beta-sheet. Here, it is reported that the beta-link is frequently found in certain protein folds of the SCOPe structural classification at specific locations where it connects a beta-sheet to another area of a protein. It is found at locations where it connects one beta-sheet to another in the beta-sandwich and related structures, and in small (four-, five- or six-stranded) beta-barrels, where it connects two beta-strands through the polypeptide chain that crosses an open end of the barrel. It is not found in larger (eight-stranded or more) beta-barrels that are straightforward beta-meanders. In some cases it initiates a connection between a single beta-sheet and an alpha-helix. The beta-link also provides a framework for catalysis in serine proteases, where the catalytic serine is part of a conserved beta-link, and in cysteine proteases, including M(pro) of human SARS-CoV-2, in which two residues of the active site are located in a conserved beta-link.
["Mechanism"]