The structure of the GemC1 coiled coil and its interaction with the Geminin family of coiled-coil proteins

Abstract

GemC1, together with Idas and Geminin, an important regulator of DNA-replication licensing and differentiation decisions, constitute a superfamily sharing a homologous central coiled-coil domain. To better understand this family of proteins, the crystal structure of a GemC1 coiled-coil domain variant engineered for better solubility was determined to 2.2 Å resolution. GemC1 shows a less typical coiled coil compared with the Geminin homodimer and the Geminin–Idas heterodimer structures. It is also shown that both in vitro and in cells GemC1 interacts with Geminin through its coiled-coil domain, forming a heterodimer that is more stable that the GemC1 homodimer. Comparative analysis of the thermal stability of all of the possible superfamily complexes, using circular dichroism to follow the unfolding of the entire helix of the coiled coil, or intrinsic tryptophan fluorescence of a unique conserved N-terminal tryptophan, shows that the unfolding of the coiled coil is likely to take place from the C-terminus towards the N-terminus. It is also shown that homodimers show a single-state unfolding, while heterodimers show a two-state unfolding, suggesting that the dimer first falls apart and the helices then unfold according to the stability of each protein. The findings argue that Geminin-family members form homodimers and heterodimers between them, and this ability is likely to be important for modulating their function in cycling and differentiating cells.

GEMC 1 is a critical regulator of multiciliated cell differentiation

“…Although these data suggest that GEMC1 acts upstream of Multicilin, it does not exclude the possibility that GEMC1 and Multicilin function together to promote MCC differentiation and potentially regulate MCC homeostasis. Consistent with this, the expression of both genes was reported to be specific to MCCs from single‐cell analysis of lung tissues (Treutlein et al , ) and we (Fig E) and others have observed an interaction between the 2 proteins that may impact their function, for example, by allowing a transition between EDG and EDM transcriptional complexes that could have distinct targets, functions or modes of regulation (Caillat et al , ).…”

“…As available data indicated that GEMC1, Multicilin and Geminin could interact through their CC domains, we next examined their relative influence on FOXJ1 activation (Caillat et al , , ). The co‐expression of Geminin with GEMC1 resulted in the near complete inhibition of FOXJ1 transcriptional activation (Fig C).…”

It's a family act: the geminin triplets take center stage in motile ciliogenesis

“…While Gemc1 and Mcidas are the major activators of MCC gene expression, Geminin suppresses this activity and thus inhibits MCC gene expression. This yin and yang of the Geminin‐Gemc1/Mcidas function appears to be a conserved feature, as Geminin is known as a negative regulator of DNA replication during cell cycle progression, whereas GemC1 and Mcidas are positive regulators of the process (Caillat et al , ).…”

Mcidas and GemC1/Lynkeas specify embryonic radial glial cells

“…34 All three members of Geminin superfamily regulate cell cycle progression and reveal similarity in their coiled-coil domain, while they interact with each other revealing high affinity in forming heretodimers. [1][2][3] Geminin is an inhibitor of pre-replicative complex formation, Mcidas regulates DNA replication and cell cycle progression through its binding to Geminin, while GemC1 mediates pre-initiation complex formation through its interactions with TopBP1 which results in the recruitment of Cdc45 and the initiation of replication. [1][2][3][4][5][6] Despite their role in DNA replication and cell cycle progression, all members of Geminin superfamily are involved on the regulation of cell fate decisions of stem cells.…”

“…[1][2][3] Geminin is an inhibitor of pre-replicative complex formation, Mcidas regulates DNA replication and cell cycle progression through its binding to Geminin, while GemC1 mediates pre-initiation complex formation through its interactions with TopBP1 which results in the recruitment of Cdc45 and the initiation of replication. [1][2][3][4][5][6] Despite their role in DNA replication and cell cycle progression, all members of Geminin superfamily are involved on the regulation of cell fate decisions of stem cells. We and others have shown that Geminin controls self-renewal and fate commitment decisions, [7][8][9] in several populations of stem cells through interactions with chromatin remodelling/ modifying complexes, suggesting that Geminin is involved in a global epigenetic regulation of crucial transcription factors.…”