From the article, my quick perusal did not catch whether the authors are referring to K1 or k2 (there is a huge difference, and many feel that they shouldn't be considered relatives even though there are some structural similarities.)
I suspect it's K2, as here is a related article...
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8308377/
14 posted on
12/04/2023 9:05:14 AM PST by
Seaplaner
(Never give in. Never give in. Never, never, never...in nothing, great or small...Winston ChurchIill)