diff --git a/src/ProteinChains.jl b/src/ProteinChains.jl
index fe3e2f7..3bb0a77 100644
--- a/src/ProteinChains.jl
+++ b/src/ProteinChains.jl
@@ -21,6 +21,7 @@ export get_atoms, get_backbone
 
 include("structure.jl")
 export ProteinStructure
+export map_chains!
 
 include("io/io.jl")
 export readcif, readpdb
diff --git a/src/structure.jl b/src/structure.jl
index c408583..4ef171b 100644
--- a/src/structure.jl
+++ b/src/structure.jl
@@ -57,6 +57,13 @@ function Base.show(io::IO, ::MIME"text/plain", structure::ProteinStructure)
     end
 end
 
+function map_chains!(f::Function, structure::ProteinStructure)
+    for (i, chain) in enumerate(structure)
+        structure[i] = f(chain)
+    end
+    return structure
+end
+
 function map_atoms!(f::Function, structure::ProteinStructure, args...)
     for chain in structure
         map_atoms!(f, chain, args...)