diff --git a/kafka/coordinator/assignors/sticky/sticky_assignor.py b/kafka/coordinator/assignors/sticky/sticky_assignor.py
index 243c26709..5e29d5894 100644
--- a/kafka/coordinator/assignors/sticky/sticky_assignor.py
+++ b/kafka/coordinator/assignors/sticky/sticky_assignor.py
@@ -6,9 +6,8 @@
 from kafka.coordinator.assignors.sticky.partition_movements import PartitionMovements
 from kafka.coordinator.assignors.sticky.sorted_set import SortedSet
 from kafka.coordinator.protocol import ConsumerProtocolMemberMetadata_v0, ConsumerProtocolMemberAssignment_v0
-from kafka.coordinator.protocol import Schema
 from kafka.protocol.struct import Struct
-from kafka.protocol.types import String, Array, Int32
+from kafka.protocol.types import Array, Int32, Schema, String
 from kafka.structs import TopicPartition
 
 log = logging.getLogger(__name__)
@@ -59,7 +58,10 @@ class StickyAssignorUserDataV1(Struct):
     """
 
     SCHEMA = Schema(
-        ("previous_assignment", Array(("topic", String("utf-8")), ("partitions", Array(Int32)))), ("generation", Int32)
+        ("previous_assignment", Array(
+            ("topic", String("utf-8")),
+            ("partitions", Array(Int32)))),
+        ("generation", Int32)
     )
 
 
diff --git a/kafka/protocol/abstract.py b/kafka/protocol/abstract.py
index e0d89433b..5817673cb 100644
--- a/kafka/protocol/abstract.py
+++ b/kafka/protocol/abstract.py
@@ -2,10 +2,12 @@
 
 
 class AbstractType(object, metaclass=abc.ABCMeta):
+    @classmethod
     @abc.abstractmethod
     def encode(cls, value): # pylint: disable=no-self-argument
         pass
 
+    @classmethod
     @abc.abstractmethod
     def decode(cls, data): # pylint: disable=no-self-argument
         pass
diff --git a/kafka/protocol/api.py b/kafka/protocol/api.py
index c7a477cac..b6b8a2996 100644
--- a/kafka/protocol/api.py
+++ b/kafka/protocol/api.py
@@ -60,11 +60,6 @@ def API_VERSION(self):
         """Integer of api request version"""
         pass
 
-    @abc.abstractproperty
-    def SCHEMA(self):
-        """An instance of Schema() representing the request structure"""
-        pass
-
     @abc.abstractproperty
     def RESPONSE_TYPE(self):
         """The Response class associated with the api request"""
@@ -96,11 +91,6 @@ def API_VERSION(self):
         """Integer of api request/response version"""
         pass
 
-    @abc.abstractproperty
-    def SCHEMA(self):
-        """An instance of Schema() representing the response structure"""
-        pass
-
     def to_object(self):
         return _to_object(self.SCHEMA, self)
 
diff --git a/kafka/protocol/group.py b/kafka/protocol/group.py
index 5d35ab219..a56bd48dc 100644
--- a/kafka/protocol/group.py
+++ b/kafka/protocol/group.py
@@ -158,6 +158,7 @@ class JoinGroupRequest_v5(Request):
 ]
 
 
+# Currently unused -- see kafka.coordinator.protocol
 class ProtocolMetadata(Struct):
     SCHEMA = Schema(
         ('version', Int16),
@@ -250,6 +251,7 @@ class SyncGroupRequest_v3(Request):
 ]
 
 
+# Currently unused -- see kafka.coordinator.protocol
 class MemberAssignment(Struct):
     SCHEMA = Schema(
         ('version', Int16),
diff --git a/kafka/protocol/struct.py b/kafka/protocol/struct.py
index b482326fa..f66170c60 100644
--- a/kafka/protocol/struct.py
+++ b/kafka/protocol/struct.py
@@ -1,3 +1,4 @@
+import abc
 from io import BytesIO
 
 from kafka.protocol.abstract import AbstractType
@@ -6,11 +7,15 @@
 from kafka.util import WeakMethod
 
 
-class Struct(AbstractType):
-    SCHEMA = Schema()
+class Struct(metaclass=abc.ABCMeta):
+
+    @abc.abstractproperty
+    def SCHEMA(self):
+        """An instance of Schema() representing the structure"""
+        pass
 
     def __init__(self, *args, **kwargs):
-        if len(args) == len(self.SCHEMA.fields):
+        if len(args) == len(self.SCHEMA):
             for i, name in enumerate(self.SCHEMA.names):
                 setattr(self, name, args[i])
         elif len(args) > 0:
@@ -23,19 +28,7 @@ def __init__(self, *args, **kwargs):
                                  % (list(self.SCHEMA.names),
                                     ', '.join(kwargs.keys())))
 
-        # overloading encode() to support both class and instance
-        # Without WeakMethod() this creates circular ref, which
-        # causes instances to "leak" to garbage
-        self.encode = WeakMethod(self._encode_self)
-
-    @classmethod
-    def encode(cls, item):  # pylint: disable=E0202
-        bits = []
-        for i, field in enumerate(cls.SCHEMA.fields):
-            bits.append(field.encode(item[i]))
-        return b''.join(bits)
-
-    def _encode_self(self):
+    def encode(self):
         return self.SCHEMA.encode(
             [getattr(self, name) for name in self.SCHEMA.names]
         )
@@ -44,7 +37,7 @@ def _encode_self(self):
     def decode(cls, data):
         if isinstance(data, bytes):
             data = BytesIO(data)
-        return cls(*[field.decode(data) for field in cls.SCHEMA.fields])
+        return cls(*cls.SCHEMA.decode(data))
 
     def get_item(self, name):
         if name not in self.SCHEMA.names: