Basically, [the reearchers] claim that a single mutation “repurposed” an enzyme that made multicellularity possible. A common guanylate kinase enzyme (gk), used by all living things to regulate the supply of nucleotides for the genetic code, underwent a mutation that enabled it to learn a new function. The new GKPIDenzyme, found primarily in animals and choanoflagellates, is important for cell adhesion and spindle orientation. The mutation gave it a new shape that enabled it to bind to a different ligand. Sometime later, GKPID found a new partner in Pins, a protein on the inner membrane that (with some helper enzymes) connects to both the spindle microtubule and the complex that receives signals from neighboring cells.
In a moment of epistemic modesty, the authors admit that their supposition doesn’t really amount to much. It’s a case of glittering generalities at best, sweetened with high hopes.
Our analyses do not establish a complete history of the spindle orientation complex. Many key steps remain to be reconstructed, including how and when the interaction between GKPID and KHC-73 evolved, the mechanisms by which Pins’ acquired its linker and GoLoco sequences, and the relationship of these components to other molecular complexes and pathways involved in animal spindle orientation. Despite these knowledge gaps, our observations establish a broad overview of the history of the GKPID complex, provide a detailed mechanistic reconstruction of a key event, and point to the importance of reusing molecules — and specific surfaces within them — for fortuitous new purposes that have the potential to become biologically essential.
Unusual for a journal paper, this one includes the dialogue between the reviewers and the authors. The criticisms and responses are well worth reading. Despite the editors’ interest in publishing this paper, they were clearly concerned about the authors’ tendency to overstate their case. More.
Yeh. The researchers’ pulpit pounding and altar calls detailed in the Evolution News & Views story were probably bad optics.
In a related development, Jell-o has just been declared a life form, in order to save the theory. Okay, it’s a bit more complex than that, but mainly due to the intervention of media releases. 😉
See also: One random mutation powers multicellular life
and
Can all the numbers for life’s origin just happen to fall into place?
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