I am looking for a protein detection tag that can be used for plate reader-based detection of protein abundance. I know there are many tags: luciferase, GFP and its variants, prolabel, etc. What are some others out there? Ideally I want something that is small and won't interfere with a protein's native stability (example: GST stabilizes proteins. I don't want that). And it needs to be structure dependent-- i.e., not an antibody paratope like V5, myc, etc. that work when denatured. I need to be able to detect a protein in cells by way of its tag but only when the protein is soluble. When the protein becomes denatured I want to lose detection.