
HGSNAT는 리소좀 내부에서 아세틸-CoA로부터 아세틸기를 헤파란 황산염의 말단 α-D-글루코사민에 전달하는 필수적인 아세틸화 반응을 촉매한다. 이 연구에서는 HGSNAT-아세틸-CoA 복합체의 고해상도 구조를 제시하고, MPS IIIC를 유발하는 돌연변이의 분자적 기반을 밝혔다.


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Degradation of heparan sulfate (HS), a glycosaminoglycan (GAG) comprised of repeating units of N -acetylglucosamine and glucuronic acid, begins in the cytosol and is completed in the lysosomes. Acetylation of the terminal non-reducing amino group of α-D-glucosamine of HS is essential for its complete breakdown into monosaccharides and free sulfate. Heparan-α-glucosaminide N -acetyltransferase (HGSNAT), a resident of the lysosomal membrane, catalyzes this essential acetylation reaction by accepting and transferring the acetyl group from cytosolic acetyl-CoA to terminal α-D-glucosamine of HS in the lysosomal lumen. Mutation-induced dysfunction in HGSNAT causes abnormal accumulation of HS within the lysosomes and leads to an autosomal recessive neurodegenerative lysosomal storage disorder called mucopolysaccharidosis IIIC (MPS IIIC). There are no approved drugs or treatment strategies to cure or manage the symptoms of, MPS IIIC. Here, we use cryo-electron microscopy (cryo-EM) to determine a high-resolution structure of the HGSNAT-acetyl-CoA complex, the first step in HGSNAT catalyzed acetyltransferase reaction. In addition, we map the known MPS IIIC mutations onto the structure and elucidate the molecular basis for mutation-induced HGSNAT dysfunction.

### Competing Interest Statement

The authors have declared no competing interest.

Structure of the human heparan-α-glucosaminide N-acetyltransferase (HGSNAT)

인간-헤파란-α-글루코사미드-n-아세틸트랜스퍼라제-hgsnat-구조


인간 헤파란-α-글루코사미드 N-아세틸트랜스퍼라제(HGSNAT) 구조


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2-옥소글루타르산은 메타노사르시나 마제이 글루타민 합성효소의 도데카머 조립을 유도하고 활성 상태로 전환시킨다.


Glutamine synthetases (GS) are central enzymes essential for the nitrogen metabolism across all domains of life. Consequently, they have been extensively studied for more than half a century. Based on the ATP dependent ammonium assimilation generating glutamine, GS expression and activity are strictly regulated in all organisms. In the methanogenic archaeon Methanosarcina mazei , it has been shown that the metabolite 2-oxoglutarate (2-OG) directly induces the GS activity. Besides, modulation of the activity by interaction with small proteins (GlnK1 and sP26) has been reported. Here, we show that the strong activation of M. mazei GS (GlnA1) by 2-OG is based on the 2-OG dependent dodecamer assembly of GlnA1 by using mass photometry (MP) and single particle cryo-electron microscopy (cryo-EM) analysis of purified strep-tagged GlnA1. The dodecamer assembly from monomers/dimers occurred without any detectable intermediate oligomeric state and was not affected in the presence of GlnK1. The 2.39 Å cryo-EM structure of the dodecameric complex in the presence of 12.5 mM 2-OG demonstrated that 2-OG is binding between two monomers. Thereby, 2-OG appears to induce the dodecameric assembly in a cooperative way. Furthermore, the active site is primed by an allosteric interaction cascade caused by 2-OG-binding towards an adaption of the transition state catalytic conformation. In the presence of additional glutamine, strong feedback inhibition of GS activity was observed. Since glutamine dependent disassembly of the dodecamer was excluded by MP, feedback inhibition most likely relies on an allosteric binding of glutamine to the catalytic site. Based on our findings, we propose that under nitrogen limitation the induction of M. mazei GS into a catalytically active dodecamer is not affected by GlnK1 and crucially depends on the presence of 2-OG.

### Competing Interest Statement

The authors have declared no competing interest.

2-oxoglutarate triggers assembly of active dodecameric Methanosarcina mazei glutamine synthetase

2-옥소글루타르산이-메타노사르시나-마제이-글루타민-합성효소의-활성-도데카머-조립을-유도한다


2-옥소글루타르산이 메타노사르시나 마제이 글루타민 합성효소의 활성 도데카머 조립을 유도한다
