The summary seems to be that opsins (proteins normally known for their role in vision) are acting to boost the signal on certain flavors indicative of potential

The summary seems to be that opsins (proteins normally known for their role in vision) are acting to boost the signal on certain flavors indicative of potentially harmful compounds, flavors that might need to be picked up in much smaller concentrations than other flavors. If I'm understanding it properly, not sure if it's a different "class" but rather a specialization for tasting bitter flavors. Wouldn't be surprised if there were similar specializations for other tastes e.g. sweetness, such as a mechanism to trigger insulin production without involving the brain.