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Cloning and sequencing of cDNAs encoding plasma alpha-macroglobulin and murinoglobulin from guinea pig: implications
H Iwasaki1, Y Suzuki, H Sinohara
1Department of Biochemistry, Kinki University School of Medicine, Osaka.
Abstract:
Several clones encoding plasma alpha-macroglobulin and murinoglobulin were isolated from guinea pig liver cDNA library and sequenced. The clones for alpha-macroglobulin contained overlapping sequences which together spanned a stretch of 4,546 nucleotides with one open reading frame coding for 1,476 amino acid residues. The clones for murinoglobulin contained overlapping sequences which together spanned a stretch of 4,578 nucleotides with one open reading frame coding for 1,464 amino acid residues. The phylogenetic analyses of 11 proteins of the alpha-macroglobulin family revealed that the mammalian tetrameric alpha-macroglobulins consist of two main branches: alpha M-1 subfamily (rat alpha 1- and mouse alpha-macroglobulins) and alpha M-2 subfamily (human alpha 2-, rat alpha 2-, and guinea pig alpha-macroglobulins). This dichotomy is in good accordance with their immunological, chemical, and physicochemical properties, and indicates that guinea pig alpha-macroglobulin is orthologous to human and rat alpha 2-macroglobulins but paralogous to rat alpha 1- and mouse alpha-macroglobulins. The divergence of the two subfamilies was a phylogenetically ancient event which occurred around the separation of metatherians and eutherians. The genes of the two subfamilies have been maintained in the rat, but either one became extinct in the mouse, guinea pig, or human. The tree also shows that guinea pig murinoglobulin forms one clade with mouse and rat murinoglobulins (alpha 1-inhibitor 3) prior to joining the alpha M-2 lineage, and suggests that murinoglobulin is not a primitive form of tetrameric alpha-macroglobulin, but rather has evolved under selective pressure which is different from that of the tetrameric paralogues.
Insights
Phylogenetic analysis reveals two distinct subfamilies within mammalian alpha-macroglobulins, with guinea pig alpha-macroglobulin belonging to the alpha M-2 subfamily. Murinoglobulin evolved separately, indicating diverse selective pressures on these protein families.
Area of Science:
- Biochemistry
- Evolutionary Biology
- Genomics
Background:
- Plasma alpha-macroglobulins are crucial protease inhibitors with diverse physiological roles.
- Understanding the evolutionary relationships of these proteins provides insights into mammalian evolution and gene family diversification.
Purpose of the Study:
- To isolate and sequence clones encoding guinea pig alpha-macroglobulin and murinoglobulin.
- To perform phylogenetic analyses of mammalian alpha-macroglobulin family proteins.
- To elucidate the evolutionary history and subfamily classification of guinea pig alpha-macroglobulin and murinoglobulin.
Main Methods:
- Isolation and sequencing of cDNA clones from a guinea pig liver library.
- Bioinformatic analysis, including open reading frame identification and phylogenetic tree construction.
- Comparative analysis of nucleotide and amino acid sequences of 11 alpha-macroglobulin family proteins.
Main Results:
- Sequencing revealed a 4,546-nucleotide sequence for alpha-macroglobulin (1,476 amino acids) and a 4,578-nucleotide sequence for murinoglobulin (1,464 amino acids).
- Phylogenetic analysis identified two main mammalian alpha-macroglobulin subfamilies: alpha M-1 (rat alpha 1, mouse) and alpha M-2 (human alpha 2, rat alpha 2, guinea pig).
- Guinea pig alpha-macroglobulin is orthologous to human/rat alpha 2-macroglobulins and paralogous to rat alpha 1/mouse alpha-macroglobulins, with divergence predating metatherian/eutherian split.
- Guinea pig murinoglobulin forms a clade with mouse/rat murinoglobulins before joining the alpha M-2 lineage, suggesting distinct evolutionary pressures.
Conclusions:
- Mammalian alpha-macroglobulins exhibit a deep evolutionary dichotomy, reflected in distinct subfamily classifications.
- Guinea pig alpha-macroglobulin's evolutionary position aligns with the alpha M-2 subfamily, distinct from alpha M-1 members.
- Murinoglobulin represents a separate evolutionary trajectory within the alpha-macroglobulin superfamily, not a primitive form, shaped by unique selective forces.