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The N-Acetylglutamate Synthase Family: Structures, Function and Mechanisms.

Shi D, Allewell NM, Tuchman M - Int J Mol Sci (2015)

Bottom Line: Recent work has shown that several different genes encode enzymes that can catalyze NAG formation.Interestingly, these bifunctional enzymes have higher sequence similarity to vertebrate NAGS than those of the classical (mono-functional) bacterial NAGS.Solving the structures for both classical bacterial NAGS and bifunctional vertebrate-like NAGS/K has advanced our insight into the regulation and catalytic mechanisms of NAGS, and the evolutionary relationship between the two NAGS groups.

View Article: PubMed Central - PubMed

Affiliation: Center for Genetic Medicine Research and Department of Integrative Systems Biology, Children's National Medical Center, the George Washington University, Washington, DC 20010, USA. dshi@childrensnational.org.

ABSTRACT
N-acetylglutamate synthase (NAGS) catalyzes the production of N-acetylglutamate (NAG) from acetyl-CoA and L-glutamate. In microorganisms and plants, the enzyme functions in the arginine biosynthetic pathway, while in mammals, its major role is to produce the essential co-factor of carbamoyl phosphate synthetase 1 (CPS1) in the urea cycle. Recent work has shown that several different genes encode enzymes that can catalyze NAG formation. A bifunctional enzyme was identified in certain bacteria, which catalyzes both NAGS and N-acetylglutamate kinase (NAGK) activities, the first two steps of the arginine biosynthetic pathway. Interestingly, these bifunctional enzymes have higher sequence similarity to vertebrate NAGS than those of the classical (mono-functional) bacterial NAGS. Solving the structures for both classical bacterial NAGS and bifunctional vertebrate-like NAGS/K has advanced our insight into the regulation and catalytic mechanisms of NAGS, and the evolutionary relationship between the two NAGS groups.

No MeSH data available.


Quaternary structure and interface interactions of ngNAGS and mmNAGS/K. Simplified model of the hexamer architecture of ngNAGS (A) and the tetrameric architecture of mmNAGS/K (B). Ribbon diagram of three different types of interface for ngNAGS: K1–K4 interface (C), K1–K5 interface (D), and S1-K3 interface (E), in comparison to those of mmNAGS/K: K1–K2 interface (F), K1–K3 interface (G), and S1–S2 interface (H). K1–K4 and K1–K5 interfaces of ngNAGS have two-fold symmetry, whose axes, indicated by a blue oval, are perpendicular to the plane. As a result, in K1–K5 interface the central β5 interacts with the equivalent β5 from another subunit in an antiparallel fashion to form a continuous β strand across this interface. No symmetry exists for S1–K3 interface of ngNAGS, which will change upon arginine binding to enzyme. All three types of interfaces of mmNAGS/K have a two-fold symmetry, indicated by blue arrows, which are parallel to the plane. As a result, the central β3 positions with the equivalent β3 from other subunit in a parallel fashion in K1–K3 interface of mmNAGS/K, which is different from that in ngNAGS. The central β18 interacts with the equivalent β18 from another subunit antiparallel in S1–S2 interface of mmNAGS/K, forming a continuous β strand across the interface. No equivalent interface is found in ngNAGS.
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ijms-16-13004-f003: Quaternary structure and interface interactions of ngNAGS and mmNAGS/K. Simplified model of the hexamer architecture of ngNAGS (A) and the tetrameric architecture of mmNAGS/K (B). Ribbon diagram of three different types of interface for ngNAGS: K1–K4 interface (C), K1–K5 interface (D), and S1-K3 interface (E), in comparison to those of mmNAGS/K: K1–K2 interface (F), K1–K3 interface (G), and S1–S2 interface (H). K1–K4 and K1–K5 interfaces of ngNAGS have two-fold symmetry, whose axes, indicated by a blue oval, are perpendicular to the plane. As a result, in K1–K5 interface the central β5 interacts with the equivalent β5 from another subunit in an antiparallel fashion to form a continuous β strand across this interface. No symmetry exists for S1–K3 interface of ngNAGS, which will change upon arginine binding to enzyme. All three types of interfaces of mmNAGS/K have a two-fold symmetry, indicated by blue arrows, which are parallel to the plane. As a result, the central β3 positions with the equivalent β3 from other subunit in a parallel fashion in K1–K3 interface of mmNAGS/K, which is different from that in ngNAGS. The central β18 interacts with the equivalent β18 from another subunit antiparallel in S1–S2 interface of mmNAGS/K, forming a continuous β strand across the interface. No equivalent interface is found in ngNAGS.

Mentions: In NAGS from N. gonorrhoeae (ngNAGS), six subunits assemble via the N-terminal AAK domains with D3 symmetry to form a toroidal shaped structure with three NAT domains on one side and three NAT domains on the other side of the hexamer (Figure 3A). Although this is the only member of the bacteria-like NAGS group with a determined structure, it is likely conserved among members of this group. paNAGS has also been shown to be a hexamer in solution [10]. In contrast to the bacteria-like NAGS configuration represented by ngNAGS, the NAGS structures of M. maris and X. campestris are tetramers in which the AAK domains of the subunits are in the middle of the molecule and the NAT domains are at both polar ends (Figure 3B). The whole molecule has a D2 symmetry, which is different from ngNAGS. Although the protein sequences are highly diverse [17], the tetrameric structure seems to be a common feature among the vertebrate-like group. Consistent with this finding, NAGK from Saccharomyces cerevisiae, has a sequence similar to the vertebrate-like group and similar two-domain structures, as well as similar tetrameric quaternary structures [48].


The N-Acetylglutamate Synthase Family: Structures, Function and Mechanisms.

Shi D, Allewell NM, Tuchman M - Int J Mol Sci (2015)

Quaternary structure and interface interactions of ngNAGS and mmNAGS/K. Simplified model of the hexamer architecture of ngNAGS (A) and the tetrameric architecture of mmNAGS/K (B). Ribbon diagram of three different types of interface for ngNAGS: K1–K4 interface (C), K1–K5 interface (D), and S1-K3 interface (E), in comparison to those of mmNAGS/K: K1–K2 interface (F), K1–K3 interface (G), and S1–S2 interface (H). K1–K4 and K1–K5 interfaces of ngNAGS have two-fold symmetry, whose axes, indicated by a blue oval, are perpendicular to the plane. As a result, in K1–K5 interface the central β5 interacts with the equivalent β5 from another subunit in an antiparallel fashion to form a continuous β strand across this interface. No symmetry exists for S1–K3 interface of ngNAGS, which will change upon arginine binding to enzyme. All three types of interfaces of mmNAGS/K have a two-fold symmetry, indicated by blue arrows, which are parallel to the plane. As a result, the central β3 positions with the equivalent β3 from other subunit in a parallel fashion in K1–K3 interface of mmNAGS/K, which is different from that in ngNAGS. The central β18 interacts with the equivalent β18 from another subunit antiparallel in S1–S2 interface of mmNAGS/K, forming a continuous β strand across the interface. No equivalent interface is found in ngNAGS.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC4490483&req=5

ijms-16-13004-f003: Quaternary structure and interface interactions of ngNAGS and mmNAGS/K. Simplified model of the hexamer architecture of ngNAGS (A) and the tetrameric architecture of mmNAGS/K (B). Ribbon diagram of three different types of interface for ngNAGS: K1–K4 interface (C), K1–K5 interface (D), and S1-K3 interface (E), in comparison to those of mmNAGS/K: K1–K2 interface (F), K1–K3 interface (G), and S1–S2 interface (H). K1–K4 and K1–K5 interfaces of ngNAGS have two-fold symmetry, whose axes, indicated by a blue oval, are perpendicular to the plane. As a result, in K1–K5 interface the central β5 interacts with the equivalent β5 from another subunit in an antiparallel fashion to form a continuous β strand across this interface. No symmetry exists for S1–K3 interface of ngNAGS, which will change upon arginine binding to enzyme. All three types of interfaces of mmNAGS/K have a two-fold symmetry, indicated by blue arrows, which are parallel to the plane. As a result, the central β3 positions with the equivalent β3 from other subunit in a parallel fashion in K1–K3 interface of mmNAGS/K, which is different from that in ngNAGS. The central β18 interacts with the equivalent β18 from another subunit antiparallel in S1–S2 interface of mmNAGS/K, forming a continuous β strand across the interface. No equivalent interface is found in ngNAGS.
Mentions: In NAGS from N. gonorrhoeae (ngNAGS), six subunits assemble via the N-terminal AAK domains with D3 symmetry to form a toroidal shaped structure with three NAT domains on one side and three NAT domains on the other side of the hexamer (Figure 3A). Although this is the only member of the bacteria-like NAGS group with a determined structure, it is likely conserved among members of this group. paNAGS has also been shown to be a hexamer in solution [10]. In contrast to the bacteria-like NAGS configuration represented by ngNAGS, the NAGS structures of M. maris and X. campestris are tetramers in which the AAK domains of the subunits are in the middle of the molecule and the NAT domains are at both polar ends (Figure 3B). The whole molecule has a D2 symmetry, which is different from ngNAGS. Although the protein sequences are highly diverse [17], the tetrameric structure seems to be a common feature among the vertebrate-like group. Consistent with this finding, NAGK from Saccharomyces cerevisiae, has a sequence similar to the vertebrate-like group and similar two-domain structures, as well as similar tetrameric quaternary structures [48].

Bottom Line: Recent work has shown that several different genes encode enzymes that can catalyze NAG formation.Interestingly, these bifunctional enzymes have higher sequence similarity to vertebrate NAGS than those of the classical (mono-functional) bacterial NAGS.Solving the structures for both classical bacterial NAGS and bifunctional vertebrate-like NAGS/K has advanced our insight into the regulation and catalytic mechanisms of NAGS, and the evolutionary relationship between the two NAGS groups.

View Article: PubMed Central - PubMed

Affiliation: Center for Genetic Medicine Research and Department of Integrative Systems Biology, Children's National Medical Center, the George Washington University, Washington, DC 20010, USA. dshi@childrensnational.org.

ABSTRACT
N-acetylglutamate synthase (NAGS) catalyzes the production of N-acetylglutamate (NAG) from acetyl-CoA and L-glutamate. In microorganisms and plants, the enzyme functions in the arginine biosynthetic pathway, while in mammals, its major role is to produce the essential co-factor of carbamoyl phosphate synthetase 1 (CPS1) in the urea cycle. Recent work has shown that several different genes encode enzymes that can catalyze NAG formation. A bifunctional enzyme was identified in certain bacteria, which catalyzes both NAGS and N-acetylglutamate kinase (NAGK) activities, the first two steps of the arginine biosynthetic pathway. Interestingly, these bifunctional enzymes have higher sequence similarity to vertebrate NAGS than those of the classical (mono-functional) bacterial NAGS. Solving the structures for both classical bacterial NAGS and bifunctional vertebrate-like NAGS/K has advanced our insight into the regulation and catalytic mechanisms of NAGS, and the evolutionary relationship between the two NAGS groups.

No MeSH data available.