Vesicle tethering and fusion promoted by LC3/GABARAP proteins is modulated by the ATG12–ATG5-ATG16L1 complex

ABSTRACT

Recently, we have examined the membrane anchoring and subsequent lipidation of six members of the LC3/GABARAP protein family, together with their ability to promote membrane tethering and fusion. GABARAP and GABARAPL1 showed the highest activities. Differences found within LC3/GABARAP proteins suggested the existence of a lipidation threshold as a requisite for tethering and inter-vesicular lipid mixing. The presence of ATG12–ATG5-ATG16L1 (E3 in short) increased and accelerated LC3/GABARAP lipidation and subsequent vesicle tethering. However, E3 hampered LC3/GABARAP capacity to induce inter-vesicular lipid mixing and/or fusion. Our results suggest a model in which, together with the recently described inter-membrane lipid transfer mechanism, LC3/GABARAP could help in the phagophore expansion process through their ability to tether and fuse vesicles. The growing regions would be areas where the LC3/GABARAP proteins could be lipidated in the absence of E3, or else an independent regulatory mechanism would allow lipid/vesicle incorporation and phagophore growth when E3 was present.

Abbreviations: Atg/ATG: autophagy-related protein (in yeast/human); E3: ATG12–ATG5-ATG16L1 complex; GABARAP: gamma-aminobutyric acid receptor associated protein; MAP1LC3/LC3: microtubule-associated protein 1 light chain 3.

KEYWORDS:

• Autophagy proteins
• autophagosome expansion
• ATG8
• ATG12–ATG5-ATG16L1
• LC3/GABARAP
• E3 complex

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported in part by the Spanish Ministerio de Ciencia e Innovación (MCI), Agencia Estatal de Investigación (AEI) and Fondo Europeo de Desarrollo Regional (FEDER) [grant No. PID2021-124461NB-I00], the Basque Government [grans No. IT1625-22], the Fundación Ramón Areces [CIVP20A6619], the Fundación Biofísica Bizkaia, and the Basque Excellence Research Centre (BERC) program of the Basque Government. MNI was a recipient of a pre-doctoral FPU fellowship from the Spanish Ministry of Science, Innovation and Universities [FPU16/05873].